WOBURN, Mass. >> The son of longtime Boston Red Sox broadcaster Jerry Remy pleaded guilty to murder and other charges for stabbing his girlfriend last year and attacking people who tried to help her, and was immediately given the mandatory sentence of life in prison without parole.

Jared Remy, 35, admitted in Middlesex Superior Court that he fatally stabbed 27-year-old Jennifer Martel in August. He described himself as “the bad apple” and called Martel “an angel” but said that he killed her one night because she had a knife and was threatening him.

Remy pleaded guilty to first-degree murder, assault and battery, and violating a restraining order, among other charges. His father, a former Red Sox second baseman who has been a color analyst on team broadcasts on the New England Sports Network since 1988, was not in court for the hearing.

Prosecutors described how Jared Remy repeatedly stabbed Martel, first in the couple’s Waltham apartment as their 4-year-old daughter screamed, and then as she crawled to an outside patio. Three neighbors tried unsuccessfully to pull Remy off Martel.

Assistant District Attorney Lisa McGovern said Remy stabbed Martel in the throat, legs, arms and torso, and pinched her face.

Before sentencing Remy, Judge Kathe Tuttman asked him if he disputed prosecutors’ account of the stabbing.

“She had a knife in her hand. She was threatening me about my daughter,” Remy told the judge in a calm voice.

Tuttman quickly moved on and accepted the plea.

Remy was initially arrested Aug. 13 after he allegedly pushed Martel into a mirror. He was released on his own recognizance and stabbed Martel on Aug. 15. He also pleaded guilty Tuesday to assaulting a man who tried to help Martel as Remy stabbed her.

A neighbor told police he tried unsuccessfully to pull Remy off Martel during the attack. Martel posted to her Facebook page the night she was killed, “Jennifer Martel is in a complicated (Relationship),” according to court documents.

An independent review criticized prosecutors’ handling of abuse allegations against Remy.

The case prompted questions about whether Remy’s violent history had been overlooked by the criminal justice system. It led state lawmakers to propose an overhaul of the state’s domestic violence laws, including new bail guidelines and tougher penalties for abusers.

Since Remy has been in jail, he has been accused of attacking another inmate, throwing hot coffee in his face, hitting him with a plastic chair and punching him. He is a former Red Sox security staffer who was fired by the team in 2008 during a steroid investigation.