Prince George’s County police have charged two teenagers with fatally stabbing a man while he was walking his dog in his Riverdale neighborhood, authorities said Wednesday.

Marcus C. Ferguson, 16, and Kenneth B. Gails, 18, both of the 6300 block of 64th Avenue in Riverdale are charged with murder in the July 14 stabbing of Glenn R. Adkisson, police said. The two teenagers were apparently trying to rob Adkisson, of the 6200 block of 64th Avenue, police said.

Adkisson was transported to a hospital in critical condition and he lapsed into a coma sometime thereafter, said Cpl. Henry Tippett, a Prince George’s police spokesman. He died Tuesday, Tippett said.

Tippett said Adkisson was stabbed in the chest, but it remains unclear who stabbed him. Ferguson is charged with first-degree murder and is being held on a no bond status. Gails is charged with second-degree murder and is being held on a $750,000 bond, police said. Both were taken into custody Tuesday evening, Tippett said.