A man convicted of negligent homicide simply walked away after leaving the Billings pre-release center at about 8 p.m. on Saturday.  25-year-old Raymond Cochran was sentenced in Cascade County on Oct. 15, 2008.  He arrived at Alpha House in January, according to a news release from Alternatives Inc.  Cochran now faces an additional 10-years for felony escape and should not be approached.