NASHUA — In a negotiated plea with state prosecutors, Ricky Munster was sentenced this week to a minimum of 28 years in prison for the beating death of a homeless man in the city.

Judge Jacalyn Colburn at Hillsborough County Superior Court accepted Munster’s guilty plea for a second-degree murder charge, sentencing him on Thursday to 28-56 years in prison for recklessly killing Mark Vallee.

Munster, 22, of Nashua, acknowledged that he beat Vallee, 51, repeatedly with his hands, feet and a two-by-four until Vallee died of blunt force trauma to the face and head on Memorial Day 2011.

Assistant Attorney General Peter Hinckley said Friday that Munster accepted responsibility for the attack, expressed remorse and assisted in the investigation.

“We felt the plea offer was fair and reasonable,” said Hinckley. “We could have gone to trial, but in light of the circumstance … the nature of the crime and the victim, we thought it was — and still is — a fair and appropriate sentence.”

According to court documents, Munster told police that he had seen Vallee fall several times and strike his head the night of the attack. Munster claimed that when he offered to help Vallee, the man took swipes at him, says court records.

Munster went on to tell authorities that he was “pissed off” at Vallee for striking him in the face, and made a statement to the effect of ,“I didn’t want to hurt him. I only wanted to help him, but he wouldn’t stop hitting me,” according to court documents.

Munster’s defense attorney, Jeremy Clemans, filed a motion to suppress the statements that his client made to police on May 30, 2011, but a judge denied that request.

In a low and crackling voice, Munster apologized to Vallee’s sister during his court appearance on Thursday, according to Hinckley.

“I can’t comment on whether it was a just sentence or not,” said Hinckley, explaining Vallee’s sister, Deborah Arthur, was not pleased with the minimum 28-year sentence.

In addition to the second degree murder charge, Munster also pleaded guilty to a separate, second degree assault charge related to an attack on an inmate at the Hillsborough County House of Corrections, according to Hinckley.

He received a 3 ½- to 7-year sentence for that incident, which will run concurrent with the lengthier sentence, prosecutors said.

Since his incarceration last year, Munster has had a string of disciplinary problems while in jail.

According to court documents, Munster has been written up for numerous misconduct behaviors, referred to as disciplinaries, while behind bars. He has been written up for alleged misuse of county property, possession of unauthorized items, profanity, threats to others, interference with security operations, violation of general rules, disobeying staff and several reports of disrespect to prison staff.

Munster, a 2008 graduate of Winslow High School in Maine, has a prior criminal record. More than a year ago, Maine police arrested Munster on two separate occasions for various offenses including concealing a knife and refusing to submit to an arrest.

Vallee, who lived on and off the streets of Nashua for more than two decades, was well known by the homeless community in the city.

khoughton@newstote.com