P.R. Laws Ap. tit. 34A, § II, Rule 238
If any of the parties shows, by affidavit, that there is a reasonable fear that any of the witnesses in a criminal action will fail to appear unless a bond is furnished, the judge acting in the preliminary investigation, or the court having jurisdiction of the case, shall order the witness to give bail in any amount he deems sufficient, and for failure to give bail, he shall order his arrest until the witness does so, or his deposition is taken. The bail undertaking shall meet the requirements fixed in these rules for defendant’s bail, and it will guarantee the witness’ attendance in any part of the court where the trial or trials are to be held, or at the preliminary hearing, on the date for which he was subpoenaed. If after being duly summoned, the witness fails to appear, the undertaking shall be forfeited in the same manner as undertakings of bail.