D.C. police detective Joseph Newell was shot and killed at his Upper Marlboro home by his stepson Monday night after a dispute over yard work, police said Tuesday.

The stepson, 27-year-old Antwan James, fled the scene of the incident but turned himself into authorities at about 6:45 p.m. Tuesday, police officials said. James is being charged with first-degree murder.

The shooting took place at about 8 p.m. Monday on the 6700 block of Green Moss Drive in the gated Avalon community.

According to a charging document, Newell came home, told James to do yard work and then headed out to the garage. James didn't do as his stepfather had asked, so his mother started yelling at him. James then stood up and said, "Oh yeah? Watch this."

James then headed outside, where Newell was screwing in a light bulb. The shooter shot his stepfather once in the back with a handgun, and Newell fell onto the driveway. James then stood on top of him and fired a few more shots, said Prince George's Assistant Police Chief Kevin Davis.

"It was an execution," said Davis.

Newell, 46, joined the District's Metropolitan Police Department in 1989, police said.

"He was a father, a husband, a son, and there's a lot of people at the Metropolitan Police Department that were out on the scene [Monday] night that are upset by this," D.C. Assistant Police Chief Peter Newsham said.

James had resigned from his job as a D.C. firefighter in August 2012.