A convicted sex offender facing charges of raping his former companion's mother killed the daughter on Tuesday and then set fire to her New Paltz apartment building, the Ulster County district attorney said yesterday. The man, Michael G. Curtis, 43, of Millbrook, was arrested on Tuesday after investigators linked him to the 29-year-old victim and found a witness who saw his car near the building before the fire, District Attorney Donald A. Williams said. Mr. Curtis, a Level 3 sex offender, considered the most dangerous, was being held without bail at the Ulster County Jail last night on a charge...