A Seat Pleasant man who fatally shot his teenage girlfriend more than two weeks after he was named in an arrest warrant — which Prince George’s County sheriffs deputies never tried to serve — has been convicted of first-degree murder.

Marcus D. Shipman, 24, was convicted by a Prince George’s Circuit Court jury on Friday of first-degree murder in the shooting death of LaCole Hines, State’s Attorney Angela D. Alsobrooks said.

Hines, 17, was fatally shot on Aug. 9, 2010, inside a liquor store in the 2600 block of Brightseat Road, in the Landover area.

Shipman was the father of Hines’s one-month old son, and had fought over his custody, authorities said. Prosecutors said Shipman lured Hines to the liquor store by telling her he would hand her the baby at that location.

Shipman shot Hines in the head inside the liquor store, authorities said. Hines was on life-support in a hospital for three days before she died.

A little more than two weeks before the shooting, Shipman allegedly threatened Hines with a handgun. An arrest warrant was issued for Shipman, charging him with first-degree felony assault, but sheriff’s deputies never tried to arrest him.

A spokeswoman for the sheriff’s department said the warrant was never entered into a computer system that sheriff’s deputies rely on. Warrants for people accused of violent offenses are supposed to be prioritized, the spokeswoman said.

But the Shipman warrant was placed by mistake in a misdemeanor file, the spokeswoman said.

The mistake involving the warrant was revealed in an article in The Washington Post as Sheriff Michael Jackson was running against Rushern L. Baker in the Democratic primary for county executive.

Baker won the primary and later won the general election.

Jackson said at the time that the mistake with the warrant was an “isolated incident.”

Circuit Court Judge Beverly Woodard is scheduled to sentence Shipman on Oct. 14. Shipman faces a maximum penalty of life without the possibility of parole, prosecutors said.