A D.C. Superior Court judge yesterday dismissed a first-degree murder charge against a Capitol Hill man arrested in the Christmas holiday slaying of Frank Flook, saying that the police had insufficient evidence to arrest him.

Judge David Norman dropped the charge against Gregory A. Benson, 27, a next-door neighbor of Flook's who was arrested March 18, nearly three months after the Dec. 27 slaying that shocked a quiet neighborhood in the 1500 block of A Street NE.

Flook and his wife, Marilyn, were the only white couple on the block of two-story row houses. The shooting so outraged neighbors and friends that they offered a $1,000 reward for information leading to the arrest of the killer.

The arrest of Benson, who lived at 1523 A St. NE, and who is a member of one of the most popular families on the block, had surprised neighbors.

Benson was arrested after a witness to the shooting picked him out in the lineup.

The 33-year-old Flook, who lived at 1521 A St. NE., was shot in the chest as he and his wife, Marilyn triedto prevent two men from forcing their way into their house about 9:30 p.m.

Just before the shooting, Flook's wife said she had partially opened the door after looking out of her bay window and seeing a male figure whom she mistook for her paper boy.

As she moved the dead bolt lock, two men began pushing the door from the outside, she said. Struggling with allher weight on the door, she screamed for her husband who was upstairs.

She said she had gotten the door almost closed when her husband came running downstairs. One of the men reached around the door with a pistol and fired, striking her husband once in the chest.

Police combed the neighborhood for witnesses and the reward was offered by Capitol Hill residents.

On March 18, police held a lineup atthe police headquarters and the undisclosed witness picked Benson from among the participants.

Joseph Benson, Gregory Benson's father, has said his son was playing cards with his sisters and friends in the family's home at the time of the shooting. Gregory Benson has maintained his innocence.