SALEM – A Peabody man who admitted he used brass knuckles to steal a $60 silver necklace and cross from a Main Street resident is headed to state prison for three years.Mark A. Acquaviva, 28, of 9 Castle Circle, changed his plea to guilty Thursday in Salem Superior Court to charges of armed robbery and carrying a dangerous weapon in connection with an August robbery.Judge John T. Lu imposed a three year state prison term, followed by five years of probation, during which Acquaviva will receive drug and alcohol treatment and counseling as deemed necessary, psychological counseling and treatment as deemed necessary. He must also submit to random alcohol and drug tests, must stay away from the victim, be employed or actively seeking employment and is not to abuse his parents.On the morning of Aug. 8 at 9:07 a.m., the victim, a 54-year-old Main Street resident, told police he was standing outside 115 Main St., near his home, when a short muscular man, wearing a white hat and shorts came up to him wielding brass knuckles and demanded he give him his silver necklace.The victim turned over the silver necklace with a silver cross worth $60 and the assailant jumped into a red Jeep Cherokee and took off.About 45 minutes later police were dispatched to 9 Castle Circle on a report of a domestic dispute.When they arrived, Acquavivas’ mother told police she was in fear and that her son came home, was in an agitated state, was in possession of a knife and brass knuckles and was downstairs.When police went downstairs, Acquaviva was gone and a door was open.Police apprehended Acquaviva nearby in the woods. He was wearing the stolen necklace around his neck, police said.In the home downstairs police retrieved the brass knuckles and knife.The victim later identified Acquaviva as the man who stole his necklace through a photo array shown to him by police.Assistant District Attorney John B. Brennan proposed a longer punishment of up to four years in prison.Defense lawyer John J. Lalikos pleaded for the lesser prison term, which Lu adopted.Acquaviva was given credit for the 223 days he’s been in custody since his arrest.