An off-duty D.C. police officer was fatally shot in Prince George's County, and police said that they have obtained a warrant for his stepson in the killing.

About 8 p.m. Monday, officers went to the 6700 block of Green Moss Drive in Upper Marlboro and found 46-year-old Joseph Burrough Newell suffering from gunshot wounds.

Newell, who joined D.C.'s Metropolitan Police Department in 1989, was pronounced dead at the scene, Prince George's County police said.

Police have identified Newell's stepson 27-year-old Antwan Rayvon James, as the suspect. He is still on the loose. According to a preliminary investigation, the shooting stemmed from a dispute over yard work.

The Green Moss Drive home where Newell and James live is in the gated Avalon community, an upscale neighborhood of about 35 houses. Neighbors said they were surprised that a homicide occurred in their community.

Police had established a barricade Monday night because they thought that James was in his home.

But early Tuesday morning, the house was cleared and the barricade was taken down.Police said that they are continuing to search for James and have obtained a warrant for his arrest.

James is described as black, 6 feet tall and 170 pounds. He was last seen wearing a white T-shirt, blue jeans and black boots, and police believe that he is armed with a gun. Anyone with information is asked to call police at 301-772-4925 or Crime Solvers at 866-411-TIPS (8477). If people see James, they should not approach him and instead should call police.