P.R. Laws Ap. tit. 34A, § II, Rule 144
The court may order the jury to be discharged before verdict in the following cases:
(a) If before the jury retires to deliberate, progress of the trial is prevented by reason of sickness or death of one of the members of the jury, unless the court decides to administer oath to another juror in substitution of the former and commence a new trial.
(b) If after the jury retires to deliberate, the progress of the trial should be prevented by reason of sickness or death of a member of the jury, an accident or any other cause to prevent their being kept together.
(c) If deliberation extends for a length of time that the court may deem sufficient to conclude clearly and manifestly that there is no possibility that the jury can agree.
(d) If any error or irregularity should have been committed during the trial which in the opinion of the court precludes the jury from returning a fair and impartial verdict.
(e) For any other cause by consent of the parties.
In all cases where a jury is discharged under the provisions of these Rules, the cause may be tried again.