SALEM – A 19-year-old Lynn man who confessed to robbing two brothers and their friend at gunpoint on Chatham Street a year ago, stealing their iPod, cigarettes and cash, will spend three years in state prison.Jonathan Monserrate, of 199 Chatham St., who was scheduled to go on trial Monday, opted to make the plea Friday afternoon in Salem Superior Court rather than stand trial before a jury of his peers.He pleaded to three counts of armed robbery while masked and three counts of assault and battery with a dangerous weapon before Judge David A. Lowy.Monserrate was sentenced to serve three years in state prison. When he is released, he will be on probation for another two years at which time he will be subject to random drug screenings, must be employed or be a full time student, must get his General Equivalency Degree (GED) and have no contact with his accusers.Shortly after 2:30 a.m. on Jan. 18, 2009, two Lynn brothers and their friend, ages 18 to 20, told authorities they had just left 7-Eleven on Essex Street and were walking down Chatham Street when a man, partly dressed all in black and wearing a bandanna covering his face, suddenly approached from behind and held a gun to one of the victims as he demanded money. The robber ordered all three men to lie on the sidewalk and took the victims’ wallets, iPod and headphones.Police were able to track his footprints left in the snow, locating Monserrate nearby.When police arrested Monserrate, they found the victims’ property on his person.A black BB gun was found ditched in a snow bank a short distance away from where Monserrate was apprehended, police said.The judge agreed to credit Monserrate the 380 days he has spent in jail awaiting trial on the case.