A 19-year-old state prison inmate admitted Tuesday he stabbed his next-door neighbor to death in Park South last summer during a fight over a radio.

Shaheem Johnson, known as “”Sha,”” pleaded guilty to first-degree manslaughter on the second day of his murder trial in Albany County Court.

He will serve between 20 and 25 years in prison for the June 24 killing of Arthur Bell, 20, outside the victim’s home on Morris Street about 6:30 p.m. The attack unfolded before a crowd of neighbors, including children, over stereo equipment that hardly worked, according to police and friends of the victim.

Johnson is serving an unrelated three-year sentence at Greene Correctional Facility for selling drugs. His new sentence will run consecutively.

Before accepting the plea deal, Johnson faced 25 years to life in prison if convicted of second-degree murder at trial. Ten jurors had been picked when Johnson pleaded guilty Tuesday afternoon.

“”Are you guilty of manslaughter in the first-degree?”” asked acting Supreme Court Justice Dan Lamont.

“”Yes,”” Johnson replied, as his mother and girlfriend sat tearfully in the courtroom gallery.

Bell’s family and friends were seated in several rows across the aisle. After the guilty plea, members of both sides exchanged words that broke into a near brawl in the hallway.

Inside, Johnson’s attorney, Michael Feit, noted his client risked a life term if convicted. He said he firmly believes Johnson did not kill Bell intentionally. “”When trials are averted, it’s sometimes for a good reason,”” Feit said. “”In this particular case, many people have been spared the ordeal … he spared his mother and his family the ordeal of having things go on.””

Authorities said the series of events that led to Bell’s death began were as follows:

Johnson and his girlfriend had a fight last year. The next day, she gave away his belongings, including giving the radio to Bell. When the couple reunited, Johnson wanted the radio back and fought with Bell over it on June 24.

Bell was walking with his girlfriend when Johnson appeared and stabbed him in the chest outside the victim’s home. Bell collapsed, and later died at Albany Medical Center Hospital.

Bell, a Schenectady native who grew up mostly in Maryland, had planned to get his general equivalency diploma and join the National Guard. He was the father of an infant son.

Johnson, who waived his right to appeal, will receive five years of post-release supervision when sentenced May 27.

The case was prosecuted by Chief Assistant District Attorney David Rossi and Assistant District Attorney Brett Knowles.