BROOKLYN - A Level 3 sex offender is back behind bars after police say he assaulted a 7-year-old Williamsburg girl in October.Police said two girls were approached by an unknown man and one was taken into an alleyway by the suspect. They say the suspect then fondled the girl.Police arrested 29-year-old Jason Forjetta on Thursday. He's being charged with sodomy, sex abuse and endangering the welfare of a child.