The widowed mother of a murdered Mattapan teen said today that walking in her own hometown was too painful to bear because of the deadly violence wrought on its streets by men like the one who killed her son.

Convicted this morning of first-degree murder for the fatal shooting of DeAndre Barboza, PATRICK GRIER (D.O.B. 7/11/88) of Dorchester was sentenced this afternoon to the mandatory punishment of life in prison without the possibility of parole.

Before that sentence was imposed, Barboza’s mother addressed the court.

“He was my golden child,” Dawn Barboza said. “I called him that because I was pregnant with him when his father, Nathaniel Rivers, was brutally murdered here in the streets of Boston …. Because of people like you, thieves of innocent life, I can’t stand to travel the streets of Boston anymore. The city I was born in, where I grew up, brings me so much pain.”

Suffolk County District Attorney Daniel F. Conley, whose office prosecuted Grier for the Dec. 1, 2008, shooting that claimed Barboza’s life, also had harsh words for the defendant.

“Dawn Barboza suffered the worst loss imaginable,” he said, “and why? For what? No motive could possibly justify this defendant’s decision to walk up to a 16-year-old boy in broad daylight, shoot him in the head, and then shoot him again as he lay on the ground. That violence, and the mentality behind it, has destroyed too many families already.”

After a two-week trial that featured almost three dozen witnesses, a Suffolk Superior Court jury found that Grier approached Barboza near the intersection of Washington and Lyndhurst streets at 9:08:52 – a time established by the video surveillance system at a nearby post office.

Assistant District Attorney John Pappas of Conley’s Homicide Unit proved that Grier fired on the youth, fired on him again after he fell to the ground, and then ran from the scene with a girl, then 16, whom he knew.

After shedding his distinctive hat on Aspinwall Street and tossing the murder weapon to his teenage associate, the evidence showed, Grier was stopped on Colonial Avenue and the female was stopped on New England Avenue.

Both resembled the descriptions provided by eyewitnesses to the shooting. The girl was carrying the murder weapon, a .22 caliber Harrington and Richardson revolver with a sawed-off barrel. Grier was out of breath, smelled of gunpowder, and could not explain his presence in the area. Subsequent testing showed gunshot residue on the cuff of his jacket and demonstrated that his phone had been used near the scene of the shooting in the preceding moments.

Barboza was transported to Boston Medical Center, where he clung to life until Dec. 3 – one day after his 17th birthday.

Presiding Judge Judith Fabricant noted that the life term for murder is mandatory under state law and called it “appropriate on the facts in this case.”

Catherine Yuan was the victim-witness advocate assigned to the case. Grier was represented by attorney David Apfel. Grier’s female associate is being prosecuted separately as an accessory to murder after the fact.