A Seat Pleasant man who fatally shot his teenage girlfriend more than two weeks after he was named in a separate arrest warrant — which Prince George’s sheriff’s deputies never tried to serve — was sentenced Friday to life in prison, authorities said.

Marcus D. Shipman, 24, was sentenced for the slaying of LaCole Hines, who was 17. On Aug. 9, 2010, Shipman shot Hines in the head at a liquor store in the Landover area.

Hines lingered on life support for a few days before she died. Hines was the mother of an infant, and Shipman was the father, according to police charging documents.

A little more than two weeks before Shipman shot Hines, he was named in an arrest warrant charging him with first-degree assault and other offenses. On July 25, 2010, Shipman allegedly yelled at Hines to come outside her apartment, then pointed a handgun at another person in the apartment stairwell, according to police charging documents.

Prince George’s sheriff’s deputies never tried to serve the warrant. Officials said it was never entered into the department’s computer system.

The sheriff at that time, Michael Jackson, was a candidate for the Democratic primary for county executive. Jackson said the mistake was “an isolated incident.” Political observers said the error was a factor in the primary victory of Rushern L. Baker III, who went on to win the general election.

“The was a case of execution,” said State’s Attorney Angela D. Alsobrooks. “Instead of finding productive ways to resolve conflict, this defendant resorted to extreme violence. Our community just won’t tolerate that kind of response to a challenging situation.”

In September, Shipman was convicted of first-degree murder and a handgun violation.

The sentence was imposed by Circuit Court Judge Beverly Woodard, officials said.