TAURO, C.J.

The defendant appeals under G.L.c. 278, §§ 33A-33G, following convictions on indictments for rape, assault and battery by means of a dangerous weapon, and armed robbery (later reduced to larceny). The Appeals Court in dismissing the rape indictment held that the defendant was not afforded a trial or other disposition of the rape charge within six months of his application for a speedy trial required by G.L.c. 277, § 72A (as appearing in St. 1965, c. 343), but refused to reverse the two remaining convictions. Commonwealth v. Gove, 1 Mass. App. Ct. 614 (1973). The case is here for further review on application of the defendant.

The defendant contends (1) that all of the indictments flow from the same incident and therefore must meet the same six months' standard under G.L.c. 277, § 72A, and (2) that, in any event, the Commonwealth has denied him his right to a speedy trial on these indictments, guaranteed by art. 11 of the Declaration of Rights of the Massachusetts Constitution and the Fourteenth Amendment to the United States Constitution. We disagree.

The incident from which all charges stem occurred in the early morning of August 8, 1969. A man broke into the apartment of the victim and removed money and a ring from her jewel box. At the time of the theft, she was asleep on the living room couch. The man awakened her, menaced her with a knife, and slapped her. He pushed her into the bedroom, and, as he did so, cut her neck slightly with his knife. In the bedroom, he attempted to have intercourse with her, but failed. After this unsuccessful attempt, she persuaded him to return her ring.

The two then emerged from the bedroom and sat down in the kitchen. The man delivered a long monologue about himself and his life. Subsequently, having finished his discourse, he ordered the victim to return to the bedroom and raped her.

Later on August 8, following a photographic identification by the victim, the Municipal Court of the Dorchester District issued a complaint which charged the defendant with the rape of the victim. No other charges were entered at that time in connection with the incident.

On April 16, 1970, while the defendant was confined to the Massachusetts Correctional Institution at Concord on an unrelated charge, he received written notification, as prescribed by G.L.c. 277, § 72A, of the pendency of the rape complaint in the District Court. Eleven days later, he filed a written application for "a prompt trial or disposition" of the rape charge. Over fourteen months later, on July 18, 1971, the defendant, by letter to the clerk of the District Court, restated his desire to go to court for a probable cause hearing or dismissal of the rape complaint.

This second communication resulted in relatively swift action by the Commonwealth. On August 15, the defendant was brought before the District Court. He was arraigned on the rape complaint and was bound over to the grand jury. On September 16, 1971, the grand jury returned indictments for rape, assault and battery by means of a dangerous weapon, and armed robbery. All indictments were related to the events of August 8, 1969. The defendant filed separate motions to dismiss the rape indictment (September 23, 1971) and the assault and battery and armed robbery indictments (September 29, 1971) for failure to grant him a speedy trial. After a Superior Court hearing at which the defendant testified, the motions were denied. The judge found, without specific reference to either the constitutional provisions or G.L.c. 277, § 72A, that the defendant had not been "actually prejudiced" by the delays in hearing his case.

On March 21, 1972, a jury found the defendant guilty on each of the three indictments.

On appeal the Appeals Court dismissed the rape indictment, holding that the more than fifteen months' interim between the defendant's application for speedy trial and his arraignment in the District Court violated G.L.c. 277, § 72A. The Appeals Court declined to dismiss the remaining indictments on the ground that no complaint, indictment or information had been "pending" at the time of the defendant's application. The Appeals Court ruled also that the defendant's constitutional claims were without merit.

I.

The statute on which the defendant relies, G.L.c. 277, § 72A, provides that penal authorities, upon learning of an "untried indictment, information or complaint . . . pending in any court in the commonwealth" against a prisoner in their custody, must advise the prisoner in writing of these untried charges. The prisoner may then make application in writing "for prompt trial or other disposition" of these charges. Under the statute, trial or other disposition "shall" occur within six months of receipt of the application by the court.

The defendant argues that the six months' period, which began with his April 27, 1970, application for prompt trial of the rape charge, must also define the time period available to the Commonwealth for adjudication of other charges flowing from the same incident. He contends that the assault and battery and robbery charges, though not brought until the September indictments were returned, must be measured against the August, 1969, to August, 1971, period relevant to the rape complaint. This, in the defendant's view, was the manifest legislative intent irrespective of the recurrent use of the word "pending." We cannot agree.

Elementary rules of statutory construction require that each statute be interpreted as enacted. Davey Bros. Inc. v. Stop Shop, Inc. 351 Mass. 59, 63 (1966). No portion of the statutory language may be deemed superfluous. Commonwealth v. Woods Hole, Martha's Vineyard Nantucket S.S. Authy. 352 Mass. 617, 618 (1967). When the statutory language is plain, the words must receive their "usual and natural meaning." Commonwealth v. Thomas, 359 Mass. 386, 387 (1971). Tilton v. Haverhill, 311 Mass. 572, 577 (1942). G.L.c. 4, § 6, Third. Statutory language should constitute the principal source of insight into legislative purpose. Commissioner of Corps. Taxn. v. Chilton Club, 318 Mass. 285, 288 (1945). The defendant's construction of G.L.c. 277, § 72A, if accepted, would require that we overlook plain statutory language and deviate from ordinary word meanings. The statutory language applies to an "untried indictment, information or complaint" which is " pending in any court in the commonwealth" (emphasis supplied). It does not apply to indictments which may emerge from further consideration of the evidence. The use of the word "pending" necessarily implies that the complaint or indictment must already exist and be awaiting action in a court. It must be a concrete charge, not a mere possibility. This view is reinforced with other specific statutory language: the correction officials must inform a prisoner of the existence of an indictment, information or complaint and of "the court in which it is pending." Even if one were to ignore the word "pending," as urged by the defendant, it is plain that the legislation requires the charge to have status before a court. The charge cannot be a prosecutorial intention. Finally, after application for speedy trial, the court must then dispose of " such indictment" (emphasis supplied). Again, the reference is to a particular prior indictment.

Thus, the statute should not be seen as a broad-gauge legislative attempt to help solve the problems underlying the concept of "speedy trial." The statute has a more restricted application. It "establishes a priority for trials of defendants who are already in custody." Commonwealth v. Stewart, 361 Mass. 857, 858 (1972). Commonwealth v. Lauria, 359 Mass. 168, 171 (1971). It furnishes a ready method for inmates to accelerate action on possible further impediments to their freedom.

We believe the statutory language bespeaks a clear legislative intention to expedite prosecution of charges already brought. The statute, in effect, is a "warrant removal" or detainer removal statute. We, therefore, reject the implication in the defendant's argument that a single indictment followed by an application for a speedy trial compels prosecutors to try or dispose of all possible charges from a single fact pattern. The application for speedy trial of the rape complaint could not affect the subsequent indictments for armed robbery and assault and battery. We do not decide any question as to the effect of the statute on successive indictments, informations or complaints relating to the same offense. See Commonwealth v. Royce, 358 Mass. 597, 599 (1971); Commonwealth v. Stewart, 361 Mass. 857 (1972). See also fns. 7, 8, infra.

II.

The Sixth Amendment to the Constitution of the United States provides that "[i]n all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial." The rights secured by the speedy trial clause are fundamental to a system of merciful and even-handed justice. Through incorporation in the Fourteenth Amendment, the speedy trial clause guarantees expeditious disposition of charges in prosecutions under State laws. Klopfer v. North Carolina, 386 U.S. 213 (1967). Commonwealth v. Lauria, 359 Mass. 168 (1971). Commonwealth v. Horne, 362 Mass. 738 (1973). A prisoner, incarcerated for another offense, does not forfeit this right solely because of his incarceration. He, too, has a vital interest in securing prompt resolution of his legal status. See Smith v. Hooey, 393 U.S. 374, 379 (1969); Dickey v. Florida, 398 U.S. 30 (1970); Strunk v. United States, 412 U.S. 434, 439 (1973); Commonwealth v. McGrath, 348 Mass. 748 (1965). Prosecutorial failure to adhere to speedy trial standards necessitates immediate dismissal of charges against the accused. Strunk v. United States, supra, at 440.

Analysis of the speedy trial guaranty divides into two related strands: a preliminary consideration of the time at which the guaranty attaches and a subsequent plenary consideration of the facts in a particular case in terms of the criteria by which the constitutionality of delays is judged. See Dickey v. Florida, 398 U.S. 30, 41 (1970).

The United States Supreme Court, in the case of United States v. Marion, 404 U.S. 307 (1971), has largely answered the threshold question concerning the timing of attachment of the guaranty. The court wrote that "it is either a formal indictment or information or else the actual restraints imposed by arrest and holding to answer a criminal charge that engage the particular protections of the speedy trial provision of the Sixth Amendment." Id. at 320. By its terms, the court observed, the speedy trial provision applies to "criminal prosecutions" in which the defendant is the "accused." The provision does not encompass the preaccusation period when a police investigation is ongoing. Commonwealth v. Jones, 360 Mass. 498 (1971). Commonwealth v. Horan, 360 Mass. 739 (1972). See Commonwealth v. Gilbert, ante, 18 (1974). Courts may not "wrench" cases from this "proper context" and language of the Sixth Amendment. United States v. Marion, supra, at 322. Thus, in the case before us, it would seem that the defendant's right to a speedy trial on charges of assault and battery and armed robbery commenced with the return of indictments against him for those charges on September 16, 1971. At that time, the Commonwealth first alleged that he had committed those offenses in the course of the episode of August 8, 1969. Prior to return of these indictments, the defendant stood accused of rape alone.

The defendant would distinguish the Marion case on the ground that the pre-accusation delay in that case occurred before any criminal charges had been proffered. He argues that all charges arising from the August 8, 1969, incident should be considered as one unit on the issue of speedy trial. He urges further that his right to a speedy trial on all offenses linked to the incident attached on the issuance of the rape complaint or, at the least, on the lodging of the warrant at Massachusetts Correctional Institution at Concord.

The defendant attempts to buttress his position by excerpting statements from the Marion opinion and applying them to his case: at the time of the complaint's issuance, he "in some way . . . [became] an `accused.'" United States v. Marion, 404 U.S. 307, 313 (1971); and after the rape warrant had been lodged against him, he was held "to answer a criminal charge." Id. at 320. Yet, the defendant refers us to no dispositive post- Marion precedent, and none has come to our attention. Accordingly, we proceed to explore defendant's contentions in some detail.

We believe the rule in the Marion case controls the instant case. Each independent charge flowing from a given incident must stand on its own. Delay prior to accusation on each charge is inconsequential for Fourteenth Amendment purposes.

Of course, if one charge should constitute a lesser included offense or a greater inclusive offense for the charge first brought, then the delay period would have to relate back to the first accusation. The second charge would be tantamount to a reaccusation on part of the first charge. See United States v. Alo, 439 F.2d 751 (2d Cir. 1971), cert. den. 404 U.S. 850 (1971), reh. den. 404 U.S. 961 (1971), cert. den. 414 U.S. 919 (1973); Stuart v. Craven, 456 F.2d 913 (9th Cir. 1972). Here, the charges of rape, assault and battery and armed robbery are distinct. They do not overlap substantially. On law and fact, this defendant could reasonably be acquitted of the rape charge without barring the others. The initial complaint on the rape charge did not necessarily implicate the defendant in these other crime categories. At the time of the complaint he had not been accused of the other crimes.

We are aided in assessing the reach of the Marion rule by the court's exposition of the purposes behind the Sixth Amendment speedy trial provision: "to prevent undue and oppressive incarceration prior to trial, to minimize anxiety and concern accompanying public accusation and to limit the possibilities that long delay will impair the ability of an accused to defend himself." United States v. Marion, 404 U.S. 307, 320 (1971), quoting from United States v. Ewell, 383 U.S. 116, 120 (1966). The court added: "Arrest is a public act that may seriously interfere with the defendant's liberty, whether he is free on bail or not, and that may disrupt his employment, drain his financial resources, curtail his associations, subject him to public obloquy, and create anxiety in him, his family and his friends." United States v. Marion, supra, at 320. An arrest on a single charge brings with it a certain quantum of anxiety, concern, economic debilitation, public scorn and restraint on liberty. For this reason, the accused is entitled to a speedy trial to resolve the issues of guilt and innocence. Yet, the arrest cannot be said to generate, in advance, further burdens on the accused owing to charges which might be brought. Prison officials cannot use potential criminal liability as a pretext for confining an inmate or for making harsher the terms of confinement. The accused may suffer anxiety and loss of reputation from an ongoing investigation or from the possibility of multiple accusations, but his damage caused by the anticipated charges does not exceed the damage permitted under the Fourteenth Amendment while in the Marion-type pre-accusation stage. Similarly, anticipated charges do not obstruct attempts to construct a defense for either past charges or new charges.

In short, the reasons which justify dismissal of indictments for post-accusation deprivation of speedy trial do not compel serious consideration of delay in a pre-accusation period during which another indictment from a single episode binds the accused. When a second set of indictments or warrants issues, they are treated for Fourteenth Amendment analysis as though their predecessor had not existed. Delay is measured from the return of indictments. In the present case, the September indictments invoked the Fourteenth Amendment speedy trial guaranty. The period prior to indictment did not affect the defendant's Fourteenth Amendment rights.

Having identified the point at which the Fourteenth Amendment speedy trial guaranty attached to the defendant's armed robbery and assault and battery indictments, we turn to the test for compliance with the speedy trial requirements of the Fourteenth Amendment. Four factors, "`[l]ength of delay, the reason for the delay, the defendant's assertion of his right, and prejudice to the defendant" must interact in a "difficult and sensitive balancing process." Barker v. Wingo, 407 U.S. 514, 530, 533. Commonwealth v. Horne, 362 Mass. 738 (1973). Commonwealth v. Gilbert, ante, 18, 21 (1974). Each factor must be accorded equal weight. The burden is on the defendant to demonstrate prejudicial delay sufficient to warrant dismissal. Commonwealth v. Jones, 360 Mass. 498, 502 (1971). Commonwealth v. Gilbert, supra, at 22. See United States v. Ewell, 383 U.S. 116 (1966). The defendant has not sustained this burden.

As we noted earlier, the defendant's right to speedy trial for armed robbery and assault and battery attached at the time of his indictment for those offenses. The delay in trial, therefore, must be measured by the interim between indictments on September 16, 1971, and trial on March 21, 1972. Slightly more than six months elapsed between indictment and trial.

In evaluating this delay, it must be considered that orderly criminal proceedings of necessity entail some delay for preparation and hearings. Acceptable delay must be proportional to the complexity of the crime and intractability of the issues. "Ordinary street crime" should go to trial more promptly than an intricate conspiracy case. Barker v. Wingo, 407 U.S. 514, 531 (1972). In the instant case, the defendant was accused of relatively straightforward offenses. The police completed their investigation shortly after the date of the crimes (August 8, 1969), and the trial transcript is a model of brevity and simplicity. Nevertheless, we do not believe a six months' delay in a time of crowded court dockets and overworked prosecutors is excessive.

The record contains scanty evidence of the reasons for the delay between indictment and trial. The defendant has not established lack of due diligence by the Commonwealth. Similarly, he has not demonstrated deliberate efforts by the Commonwealth to postpone trial. The judge expressly found that no portion of the delay from rape complaint to motion hearing resulted from the intentional actions of the Commonwealth. There is no allegation that docketing was unreasonably deferred. At the time, the defendant did not protest or demand a more expeditious hearing. The delay may well have resulted from the congested dockets in the Superior Court, but this, in and of itself, does not justify unreasonable delay.

Such explanation for the delay does not count heavily in favor of the defendant. Though the Commonwealth must shoulder some responsibility for the turgid court docket (see Barker v. Wingo, supra, at 531), the defendant must share the over-all responsibility for the hiatus between indictment and trial. His motion to dismiss resulted in a hearing in the Superior Court and, undoubtedly, set back the trial date. Cf. Commonwealth v. Gilbert, supra. We cannot quantify the responsibility apportioned to each party. However, on this record, we treat reasons for the delay as a factor which provides some very limited support for the defendant's Sixth Amendment claim.

The defendant did not attempt to accelerate progress from indictments to trial with a specific demand for speedy trial. Failure to demand speedy trial does not automatically cause waiver of the speedy trial right. Commonwealth v. Horne, 362 Mass. 738, 741-742 (1973), citing Barker v. Wingo. Rather, the court must consider demand or lack of demand to be an indication of the severity of prejudice to defendants. As the Supreme Court wrote, "The more serious the deprivation, the more likely a defendant is to complain." Barker v. Wingo, supra, at 531. For this purpose, we view the defendant's motion to dismiss as the functional equivalent of a specific demand for speedy trial on the armed robbery and assault and battery indictments. It is sufficiently emblematic of concern.

The final factor, prejudice to the defendant, does not materially aid the defendant. In his brief, he relies on the effect of the long delay from rape complaint to trial. He asserts that delay impeded his rehabilitation, depressed him, and cost him an opportunity for concurrent sentencing. He claims that the victim's identification "necessarily" became less reliable as time elapsed.

Consistent with our earlier statements, we decline to consider prejudice suffered because of preindictment delay. The defendant has not demonstrated substantial prejudice owing to postindictment delay. It is true that the certainty of eyewitnesses erodes as years pass. See United States v. Butler, 426 F.2d 1275, 1277 (1st Cir. 1970), cert. den. 401 U.S. 978 (1971). This loss of memory does not always appear clearly etched in the record. Barker v. Wingo, supra, at 532. Yet, such gaps in the proof may redound to the defendant's benefit. If prosecution witnesses cannot recall events with sufficient clarity to convince the jury, the defendant will be acquitted. The defendant must, therefore, substantiate his claim that delay prejudiced his defense. United States v. Ewell, 383 U.S. 116, 122 (1966). United States v. Alo, 439 F.2d 751, 755 (2d Cir. 1971), cert. den. 404 U.S. 850 (1971), reh. den. 404 U.S. 961 (1971), cert. den. 414 U.S. 919 (1973). Cf. Barker v. Wingo, 407 U.S. 514, 534 (1972). On the record before us, we are not persuaded that delay in trying the indictments precluded the defendant from making his best defense. He presented no witnesses whose memory had become fogged. He suggested the name of no witness who had died or moved away in the interim. Cf. Dickey v. Florida, 398 U.S. 30, 38 (1970); United States v. Macino, 486 F.2d 750 (7th Cir. 1973). In fact, the defense rested after the conclusion of the prosecution's case in chief.

The defendant, himself, did not testify. Nothing in the record leads to the conclusion that his failure is attributable to a lapse of memory caused by the passage of time. Quite the contrary, the judge found "that the defendant's memory on April 27, 1970 as to the events of August 8, 1969, was no better (and presumably would have been no better within six months after that date) than it is today."

The Commonwealth's case could have been prejudiced by delay. The prosecution's "star witness," the victim, was an eyewitness, whose memory could have faded. Any uncertainty on the witness stand would have greatly undermined her credibility with the jury. Yet, she made a positive identification in court and was not discredited or shaken in her testimony by cross-examination. We see no prejudice to the defendant in the trial.

Similarly, there is no convincing argument that the defendant suffered material prejudice in his conditions of confinement. Generally, delay in trial of untried indictments may deprive an inmate of opportunities for parole, concurrent sentencing and rehabilitation. Smith v. Hooey, 393 U.S. 374, 378 (1969). Strunk v. United States, 412 U.S. 434, 439 (1973). Moore v. Arizona, 414 U.S. 25, 27 (1973). See Commonwealth v. Green, 353 Mass. 687 (1968). The prospect of an extension of sentence, posed by an untried charge, may subject the inmate to great stress or anxiety. Strunk v. United States, supra. The defendant Gove has presented no evidence that this has indeed been his plight as a result of the indictments at issue here. His brief refers to the general possibilities for prejudice mentioned above. It does not particularize those possibilities or apply them to this defendant or those charges. The element of prejudice to the confined prisoner, thus, remains speculative and insubstantial. See United States v. Ewell, 383 U.S. 116, 122 (1966). In the light of the relatively short six months' delay and absence of contrary proof, we conclude there was no material prejudice to the defendant.

Accordingly, we hold that the Commonwealth did not deny the defendant a speedy trial in contravention of his Fourteenth Amendment and art. 11 rights.

Judgments affirmed.