BROOKLYN NEWS. An Accomplice of Booth. A few days since a young man, whose name has not been divulged, was arrested by Detective Frost and others on the charge of theft, and, proving to be a smart fellow, told something more than he knew to be the facts in order to emulate himself from the actual offences of which it was alleged he was guilty. He stated that he knew the assassin Booth, having acted as an errand boy, etc. and said that Harrold (sic) had been a resident of Brooklyn and an attendant of a physician who formerly resided here. The officers believing that he knew something of the assassination, and having an eye to the reward, kept him in custody for some days, and reported the case to the General Superintendent Kennedy of the Metropolitan Police. That officer examined the matter thoroughly, and, as recorded, found it to be "bosh" and ordered the young man's release. He is still held, however, upon the charge which he was originally arrested.