D.C. police are investigating three killings that occurred within a six-hour period starting Thursday night.

The first slaying was discovered shortly after 9 p.m., when police found an unidentified man suffering from stab wounds in an apartment in the 100 block of Gallatin Street NW. The man was taken to D.C. General Hospital, where he was pronounced dead at 2:30 a.m. His identification was withheld pending notification of relatives.

Two men were found shot on the street in the 4900 block of F Street SE. Police said the men were standing on the street about 1 a.m. yesterday when at least two people approached them, one of whom brandished a handgun and demanded money. The victims complied but were shot anyway, and the assailants fled in a blue car, police said.

The victims were taken to D.C. General, where one was pronounced dead at 2:02 a.m. The other man was treated and released, police said.

At 3 a.m. yesterday, a man was shot while driving in the 1600 block of Brentwood Road NE, police said. Gunmen in two vehicles opened fire on a third car driven by Nathaniel Holmes, 18. Holmes was shot at least once but continued driving. He then hit a parked car in the 1000 block of New York Avenue NE, got out of his car and collapsed, police said.

Holmes, of the 3100 block of 15th Place SE, was taken to D.C. General, where he was pronounced dead at 5:30 a.m.