Police on Friday arrested a convicted sex offender suspected of abducting a 13-year-old at knifepoint and sexually abusing him before leaving him undressed and handcuffed to a tree.

A tip led police to the 26-year-old man, whose photo was identified by the boy, said Lt. Robert Sprague. Investigators later found the boy's bracelet and his cell phone at the suspect's Staten Island house, he said. Charges were pending in the case.

The boy was heard screaming for help by a passer-by early Wednesday and was rescued by authorities. Police initially doubted the boy's story that a stranger had accosted him while on his way to the school bus because of conflicting details.

They investigated the possibility that he had met someone on the Internet and arranged a meeting, but on Thursday a woman called saying a man had admitted accosting the boy, authorities said.

Investigators said the man had a 1999 conviction for sodomy and endangering the welfare of a child.

Police said the suspect also was involved in the attempted abduction of a 14-year-old boy on Staten Island on March 5.