A Southeast Washington teenager charged in an ambush-style assault on one of his friends is being questioned about a similar attack one block away on Monday night that left his girlfriend and her roommate dead, according to police and court records.

Marquette Johnson, 19, the boyfriend of Natosha Adams, is being interviewed about the slayings of Adams, 17, and her best friend, Melissa Payne, 16, after he was booked on a charge of assault with intent to kill in a seven-bullet assault on one of their friends, according to police and court records.

Police are hesitant to draw the triangle that would connect Johnson to a motive in both shootings, though they hinted that an interview with Johnson might be fruitful.

"We're very happy to have him," Police Chief Charles H. Ramsey said yesterday.

The bloodshed began in the 200 block of 37th Street SE about 2 a.m. Monday, when Marquis Henderson was shot in the leg, arm, neck and chin, according to records at D.C. Superior Court.

He told police the shooter was a young man he had known for more than a year as " 'Quette."

Henderson was taken to D.C. General Hospital, and officials there declined to release any information about his condition.

According to an arrest warrant filed yesterday in Superior Court, when police showed Henderson a photograph of the 5-foot-7, 154-pound Johnson, Henderson immediately said, "He shot me."

After his arrest, Johnson told a court interviewer that he is the unmarried father of one child and does not use drugs. He said he attends Anacostia High School and has been living with his mother for six years. He has had no criminal convictions since he turned 18.

Johnson's mother, however, told the court that Johnson is not in school and was not living with her. His mother, who declined to be interviewed, told another person that Johnson had been living with Adams, whom she described as his girlfriend. Johnson appeared yesterday in D.C. Superior Court, where defense lawyer Joanne D. Slaight argued unsuccessfully that Johnson should be released to his mother, who offered to take him in. A court commissioner ordered him held without bond until a Jan. 7 hearing.

Police are questioning Johnson about the slayings of Adams and Payne, which occurred in the 300 block of 37th Street SE the night after Henderson was shot.

Adams and Payne were living one building away from their families, in an apartment left empty when Adams's sister moved out, family and neighbors said.

They came home about 11:30 p.m. Monday after dropping off one last round of late Christmas presents. Sheri Adams, Adams's sister, let the two out of the car and headed back to her new home on Rhode Island Avenue, said Jacqueline Adams, mother of Natosha and Sheri.

The teenagers were attacked as they headed to their first-floor apartment.

Payne was shot on the walkway and died two hours later. Adams was chased into the apartment building, where she was shot eight times. She was pronounced dead at the scene, police said.

On Wednesday, Ramsey demoted the lieutenant in charge of homicides in the 6th District and reassigned three detectives on the case when he learned that several mistakes had been made in the investigation.

No detectives were present at the autopsies, Ramsey said. Sources said the chief was particularly upset that only some of the shell casings were collected initially at the crime scene Monday night.

Officers complained yesterday that the district is understaffed, a problem Ramsey acknowledged but discounted as an excuse.

"The mistakes that were made had nothing at all to do with staffing," Ramsey said. "They all could've been avoided."