A convicted sex offender has pleaded guilty to repeatedly using phony credentials to gain entry into New York City jails.

The 36-year-old Yonkers resident Matthew Matagrano pleaded guilty Thursday to posing as a correction officer and sneaking into the Manhattan Detention Center.

During one of those visits, on Feb. 27, Matagrano assaulted an inmate and stole a $2,500 walkie-talkie. He also handed out cigarettes to inmates.

It's not clear why the former inmate, whose rap sheet includes a conviction for sodomy and sexual abuse, wanted to get back into jails.

He faces 10 years behind bars at sentencing.