SALEM – On a hot summer day in 2007 a homeless Lynn man stole a case of Heineken beer off a delivery truck and then confronted the delivery man at knifepoint when he tried to get it back. Now it is going to cost him three years behind bars.George Halfkenny, 37, apparently known for living on the streets of Lynn, changed his plea to guilty Thursday morning in Salem Superior Court, admitting to a charge of armed robbery and was sentenced to serve two to three years in state prison by Judge Howard J. Whitehead.It was around 10 a.m., on Aug. 2 when Juan Salcedo, 40, of Danvers, was unloading beer for Merrimac Valley Distributors onto pallets at a scheduled stop on Union Street.As he was exiting the store after delivering some of the cases, he noticed a case of Heineken was missing and saw a man carrying a case of Heineken beer down the street.Salcedo began chasing the suspect onto Essex Street, catching up with him in the parking lot of a business at 274 Essex St.In the meantime, Halfkenny pushed the case underneath a parked car when he saw Salcedo.When Salcedo went to retrieve the case of beer, Halfkenny pulled out a knife, gesturing forward towards Salcedo, who backed off and immediately pulled out his cell phone and called police.Halfkenny took off, leaving the case of beer behind.Police quickly responding to the scene arrested Halfkenny about 15 minutes later on Fayette Street.Salcedo later identified Halfkenny as the thief he confronted in a line-up.Assistant District Attorney Karen H. Hopwood argued for a longer punishment, suggesting four-to-six years in prison based on his “extensive record dating back two decades,” involving cases of assaultive behavior.She also told Whitehead that she spoke to Salcedo and he supports her recommendation.Defense lawyer Joseph F. Collins pleaded for a more lenient penalty of two years, while telling Whitehead his client wants to “start anew,” and is tired of the life he had led.In handing down the sentence, Whitehead acknowledged that his record was “horrible.”He said the commonwealth’s recommendation was appropriate, but felt the case itself fell between a larceny assault and battery and an armed robbery case.”The character of the offense,” Whitehead said, reflects the sentence he was imposing.The judge credited Halfkenny the 445 days he has been held awaiting trial in the case.Halfkenny went to trial earlier this year on the case and was found guilty by a jury, but due to a legal technicality involving jury instructions by Judge David A. Lowy, he overturned the verdict and ordered a new trial.