Three people were shot and killed and a fourth was critically wounded in the District last night in three separate incidents that occurred within a mile of each other.

Police investigators said they knew of no connection among the incidents, which occurred during a three-hour period near the southern tip of the District.

As of early this morning, the identities of the victims had not been released and no arrests had been reported.

The first victim, a man believed to be about 50 years old, was found fatally shot in an apartment in the 4300 block of Halley Terrace SE.

Police, called to the scene at 7:12 p.m., said the the door of the apartment was open. The man had been shot with a large-caliber weapon, and a sawed-off shotgun was found in a nearby hallway, one investigator said.

Seven minutes after the first call, officers were summoned to the 3900 block of Second Street SW, about a half mile away.

They found a victim, described by witnesses as appearing to be in his teens or early 20s, who had been shot in the head. Witnesses said he was lying between the curb and sidewalk.

The third of the shootings occurred about 9:30 p.m. inside an apartment house in the 4900 block of Martin Luther King Jr. Avenue SW, less than a mile south of the Second Street site.

A man had been shot to death on a stairway landing of the building and a woman was critically wounded.

The woman was taken to Washington Hospital Center by helicopter. She arrived at 10:17 p.m., and was taken immediately into surgery, a hospital spokeswoman said.