SALEM – A Lynn laborer who admitted stealing a purse containing about $65 from a female outside a pub in downtown Salem in the winter of 2009 and striking a man who tried to intercede is headed to state prison for three years.Adam Greenleaf, 27, of 2 Murray St., Lynn, changed his plea of innocent to guilty to charges of unarmed robbery, assault and battery and intimidation of a witness Thursday afternoon in Salem Superior Court before Judge John T. Lu.He was sentenced to serve three years in state prison to be followed by another three years of probation at which time he will be evaluated for substance abuse treatment and counseling as deemed necessary, consent to random screenings, not have contact with the victims and must have full-time employment, be in school or have two pending job applications on file.Assistant District Attorney Karen Hopwood said the charges arise out of an incident on Jan. 9, 2009.The 21-year-old female told authorities she was outside the Washington Street establishment smoking a cigarette when the suspect approached her and asked if she had another cigarette. As she took out her purse to fetch the cigarette, Greenleaf grabbed her purse and began to run off. A concerned onlooker tried to intercede and was physically struck and threatened by Greenleaf as he made his escape.Greenleaf was arrested following an investigation.In asking the judge to adopt the joint recommendation proposed, defense lawyer Joseph F. Collins told Lu that his client had enrolled in school, been participating in sports programs at the jail and also has enrolled in several sobriety programs.The sentence imposed will coincide with a punishment Greenleaf is now serving on an unrelated motor vehicle crime out of district court.An Essex County grand jury indicted him in December of 2009.