A convicted sex offender is behind bars for allegedly tying up and stabbing his girlfriend Saturday in Nyack.

Police arrested 44-year-old Thomas Dorsey and his friend 36-year-old Michael Coyle. Investigators say Dorsey?s girlfriend sold Coyle's cell phone to get money for crack. When the two men found out about it, Coyle tried to track down the phone. Police say Dorsey started attacking his girlfriend, stabbing her with a switchblade and when Coyle came back he used a rope to tie up the woman.

The 35-year-old woman was taken to Nyack Hospital. Both Dorsey and Coyle are being held at Rockland County jail without bail. Police say they are also looking into charging Dorsey for not registering as a sex offender in the Town of Orangetown.