Neighbors of a Capitol Hill man charged with the Christmastime slaying of his next-door neighbor, Frank Flook, yesterday expressed shock at the news of the man's arrest.

"It was quite a blow to the neighborhood," said Rita Yates, a neighbor of Gregory Benson who was charged with the first-degree murder of Flook. "Everybody right now is so hurt. Everybody feels for the family. What can you say?"

Benson, 27, of 1523 A St. NE, was arrested at his home Tuesday night after a witness picked him out of a court-ordered lineup at police headquarters earlier that evening, police said.

The 33-year-old Flook, who lived next door at 1521 A St. NE, was shot once in the head as he and his wife Marilyn tried to prevent two men from forcing their way into their house last Dec. 27.

Yesterday, a D.C. Superior Court judge released Benson to the custody of his father and ordered him to return to court today for a forensic examination.

The shooting of Flook outraged friends and neighbors who offered a $1,000 reward for information leading to the arrest of the killer. No one has claimed the reward.

Neighbors on the quiet street of two-story row houses yesterday expressed surprise at the arrest of Benson, a member of one of the most popular families on the block.

"I hope they [the police] made a mistake," said one man who has been in the neighborhood for more than 30 years.

"That's terrible," Pauline Patterson, another neighbor, said when told of the arrest. "Oh my God."

Neighbors said Gregory Benson had grown up in the neighborhood and was quite friendly. Some elderly neighbors said he always was polite and respectful to them.

"I just saw him the other day," said William Parker Sr. "I had been ill and he asked me how I was getting along. He seemed all right."

Benson attended D.C. public schools before dropping out of the 12th grade at Eastern High School, his father said. He had worked at odd jobs and had been unemployed since last November.

Willie Evans, manager of a service station at 14th Street and Maryland Avenue NE, where Benson last worked, said Gregory Benson "was a good worker . . . I just don't think Greg would do something like that."

Joseph Benson, the suspect's father, said yesterday, "I can't quite understand it. I just can't figure it out. It's got me thrown."

Benson said Gregory, the eldest of seven children, was playing cards with his sisters and friends in the family's home at the time of the shooting.

The elder Benson said he understood that his son had been picked out of a lineup by the victim's wife, but police refused to say who the witness was.

"I'm concerned if they are going to charge Gregory with something like this," he said. "It has been 2 1/2 months and he's been in and out of here all that time. You mean it would take 2 1/2 months to identify him?"

According to the affidavit for Benson's arrest, the witness observed the court-ordered lineup at 6:27 p.m. Tuesday. The witness stated, "No. 9 looks like the person."

The witness later told police that the person wearing shield No. 8, which was worn by Gregory Benson in the lineup, was one of the two men who tried to force their way into the house at the time of the shooting.

The witness was unable to say which of the two fired the fatal shot, the affidavit stated. But under the law, if a murder is committed in the course of a crime, all those who committed the crime are considered to be guilty of the murder.

Police yesterday said Benson had been a suspect ever since the shooting. On the basis of further investigation, information from other neighbors who reported seeing Benson near the Flook house around the time of the shooting, and the lineup, police said they arrested Benson.

A grand jury currently is hearing evidence in the Flook shooting and most of the neighbors have appeared before the grand jury in recent days. The Benson family was summoned yesterday to appear before the grand jury today.

Marilyn Flook yesterday declined to comment on Benson's arrest. "It's not the right time," she said. Flook said she had been staying with friends on the advice of the police.

Police said they were continuing to search for a second suspect.