In slow motion, the surveillance video shows a group of young men walking the aisles of the 7-Eleven shortly after 3 a.m. Sunday.

Moments later, members of the same group are seen outside the Suitland store, with at least one of them crouched in a fighting stance ready to strike Michael Antonio Bassett, 18. And then, a rain of fists, said police sources who have seen the videotape that captured images of Bassett's attackers and the initial beating that preceded his death.

While authorities worked yesterday to enhance the grainy color video so that they could show it to witnesses, investigators continued to interview those who were at the store and follow the many leads that have poured in since Sunday.

Cpl. Diane Richardson, a Prince George's County police spokeswoman, said the number of calls to the department's tip line has "encouraged the detectives."

"The community's response has been the type of response we hope for on every case," she said. "The community is upset by this murder, and the police department is troubled by it, too."

Bassett, a senior at Oxon Hill High School who was one week from graduation, was beaten, kicked and then left alone on a heavily traveled road, where police said at least two cars struck him. He was pronounced dead at the scene about 3:30 a.m., not far from the 7-Eleven in the 5400 block of Silver Hill Road where he and two friends had stopped for cold drinks 15 minutes earlier, after a night of dancing.

Authorities said Bassett and his friends were attacked because one of the assailants was enraged that Bassett had offered to buy a Slurpee for a girl standing outside the store. They said they are investigating the possibility that the young man who instigated the beating knew the girl or had a relationship with her.

Even after Bassett rescinded his offer and apologized, he and his friends were accosted, Richardson said. As many as eight youths pursued them, she said, with gunshots fired at some point.

Officials said yesterday that they had not determined whether Bassett died from the beating or from the cars running over his body. Autopsy results from the state's medical examiner's office were not complete, and the case remained open, said Karen V. Poe, a spokeswoman for the office.

Richardson said Bassett's friends were hit with fists but suffered no serious injuries. Their names were not released because they are witnesses.

At Oxon Hill High School, a crisis team consisting of a guidance counselor and other staff members talked with students yesterday about their feelings and memories of Bassett, said Lynn McCawley, a spokeswoman for Prince George's County. She also said the principal, Ronald Curtis, would be sending letters home to parents notifying them that Friday's graduation practice and picnic would be rescheduled so that students and teachers could attend Bassett's funeral.

The school's seniors finished classes May 21 and weren't at the campus yesterday but will return later in the week for graduation rehearsals.

Richardson, the police spokeswoman, said investigators will follow every clue until the case is closed.

"We continue to ask for help, and we urge the suspects to turn themselves in," she said. "The bottom line is we have a young man who offered only to buy a girl a Slurpee, and now he's dead."

Richardson asked that anyone with information about the case contact authorities at 1-800-673-2777.

Staff writer Nancy Trejos contributed to this report.