Upon a specific or general request of the officer commanding any friendly foreign force, having service courts of appropriate jurisdiction within the United States, it shall be lawful for any person in the civil, military, or naval establishments of the United States having authority to arrest, summarily to arrest any member of such force designated in such request and to deliver him to the custody of any officer of such force or to the custody of the military or naval authorities of the United States who shall deliver him forthwith to the custody of an officer of such force, for trial in such service courts within the United States for such offenses as shall lie within the jurisdiction of the service courts of such friendly foreign force: , That the trial of any member of such friendly foreign force for an offense against a member of the civilian population shall be in open court (except where security consideration forbids), shall take place promptly in the United States and within a reasonable distance from the place where the offense is alleged to have been committed, for the convenience of witnesses.Provided