An off-duty deputy U.S. marshal embroiled in an apparent road rage confrontation along Rockville Pike on Thursday night fired repeatedly into the rear window of his adversary's car, killing the man as he sat behind the wheel, according to police and witnesses.

Numerous witnesses to the death of Ryan T. Stowers, 20, at the Mid-Pike Plaza in Rockville shortly before 8:30 p.m. were being interviewed by Montgomery County police yesterday. Authorities said no decision had been made on whether charges would be filed against Arthur L. Lloyd, 53, a 28-year veteran of the U.S. Marshals Service assigned to U.S. District Court in Washington.

"The rear window was shattered out," said Capt. John Fitzgerald, a police spokesman, who said investigators had begun to talk with at least 40 witnesses. "With that many witnesses, there ought to be a very clear picture of what went down."

Although Fitzgerald said Stowers may have driven toward the federal agent in the plaza parking lot, three people who said they witnessed the shooting told The Washington Post that Lloyd was standing with his gun drawn and opened fire after Stowers drove past him.

David Sacks, a spokesman for the U.S. Marshals Service, said the federal agency will decide Monday whether Lloyd, who was not at work yesterday, would be placed on leave during the investigation by Montgomery police.

"We will wait with everyone else for the facts of the case to become known," Sacks said. "Regarding what happened, we cannot comment until the investigation is complete."

Lloyd could not be located to comment.

Stowers, of Redding, Calif., enlisted in the Navy and had moved to the area on Navy business. A Navy spokesman yesterday would not provide any information about him.

The confrontation began in the thick evening traffic on Rockville Pike, a four-lane artery known for its routine congestion, and played out in the large, well-lighted Mid-Pike Plaza parking lot, about six miles north of the District line.

The following account of the incident was drawn from preliminary police reports, law enforcement sources and interviews with witnesses.

The altercation was sparked by a traffic incident on Rockville Pike and continued after Stowers and Lloyd turned into the shopping center lot. It is unclear whether the vehicles collided or the two drivers merely had a traffic argument.

Stowers pulled his red Chevrolet Camaro into the lot, not far from the A.C. Moore craft store, behind the dark-colored sport-utility vehicle that Lloyd was driving, with his wife and several children as passengers.

A shouting match turned into a fistfight, and Lloyd suffered a broken thumb, according to one source familiar with the investigation who declined to be identified because the investigation is not complete.

Cindy Nachman-Senders of Potomac said she heard shouting in the crowded parking lot as she strapped her 5-year-old son into his booster seat. She turned to see two men in a confrontation beside their stopped vehicles.

She said Stowers got into his car and was on his cell phone. She said Lloyd started yelling: "Give me the cell phone! I'm going to call 911!"

A witness who said he was driving in the opposite direction in his Toyota Corolla at that point said he saw a man who was wearing street clothes holding a semiautomatic handgun and a badge standing by the Camaro's right front fender. The driver's window was down, he said.

"I noticed that the officer was standing in front of the Camaro, pointing his gun and saying, 'Get out of the car, or I'm going to shoot you!' He was yelling it very loudly," said the Toyota driver. He spoke on the condition that his name not be used because he was afraid of getting in trouble with the police. He said the man with the gun "just kept yelling. He was saying, 'You just hit a federal officer. Watch what's going to happen to you in the morning if you leave.' "

Stowers refused to get out of the car, the Toyota driver said. "The young man in the car was yelling: 'I need a picture ID. Show me a picture ID. I don't believe you,' " he said.

Another person who said she witnessed the incident, Eugenia Hull of Silver Spring, also said she heard Lloyd order Stowers to "get out of the car." She said Lloyd responded to the request for additional identification by saying, "That's all the ID you're going to get."

Witnesses agree that Stowers attempted to drive away, although there is not agreement on whether he moved in reverse or tried to swerve around Lloyd.

Fitzgerald, the police spokesman, said preliminary interviews indicated that Stowers "drove away in the direction of the deputy marshal . . . but we'll accept any fact pattern that changes this." He said investigators "would have to determine where [Lloyd] was and how far away from the car he was" when the shots were fired.

As Nachman-Senders saw it, Stowers reversed the Camaro, gunned the engine and then went around the SUV, not at it. "He was trying to leave the scene, not hit the officer," she said.

Hull described Stowers as trying to "move around" Lloyd when she heard the shots.

The Toyota driver said he had just eased his own car by the confrontation when the Camaro backed up and then lurched forward. He said he was about eight feet away when he heard the first of three shots, and he said that Lloyd fired into the Camaro from the rear.

"He shot the back of the car," the driver said. "He shot the guy in the back, pretty much."

Nachman-Senders said she turned back to Lloyd, who stood with the gun at his side. Then she heard a loud crash. She turned toward the noise and saw that the Camaro had hit a wall.

"I'm just in shock and disbelief. I can't believe there's a kid who was here one minute and then not the next," she said. "I can't believe that an argument could escalate this way so quickly. . . . How responsible was it for him to shoot like that in the middle of a busy parking lot?"

Staff writers Jamie Stockwell, Nicole Fuller, Rebecca Dana and Darragh Johnson and staff researcher Bobbye Pratt contributed to this report.

Montgomery County investigators survey the scene of the shooting in a shopping center parking lot along Rockville Pike.