When a person, by virtue of a subpoena, attends before a judge or a court as a witness for The People or for the defense and is poor and unable to pay the expenses of such attendance, the court, in its discretion, may direct the clerk of the court to pay the witness a reasonable sum, which shall not exceed the per diem assigned to him and which shall be charged against his per diem. The order of the court shall be in writing, but it may be issued in open court, in which case it shall be entered in the minutes.
Puerto Rico Legal Code