— Once again, police rushed to the campus of Virginia Tech. Again, the words man with a gun raced across the university. And again, students and workers locked doors and turned off lights.

But a day-long search Thursday failed to locate the tall figure in the blue-and-white vertically striped shirt whom three summer campers thought they saw with a pistol, and by late afternoon their report remained unconfirmed.

A five-hour campus lockdown was lifted shortly after 2:30 p.m.

Still, this was Virginia Tech, where in 2007 a deranged student armed with two handguns killed 32 people and himself, and such reports resonate as perhaps nowhere else.

“We’re in Blacksburg,” said Alex Watt, 19, a sophomore from Springfield, who was on campus Thursday. “And because of the history, it makes it scarier.”

The initial report came about 9 a.m., when three 14-year-old girls attending an academic summer camp said they saw a 6-foot-tall white man, in gray shorts and sandals, walking quickly with what looked like a handgun concealed by a cloth.

Text and e-mail alerts went out quickly across the university, which was populated by only a few thousand summer school students, athletes, and researchers and other employees. Staff members went through buildings to spread the alert.

“Person with a gun reported near [dining hall],” an alert posted at 9:37 a.m read. “Stay Inside. Secure doors. Emergency personnel responding. Call 911 for help.”

The university also asked anyone with information to call a campus police tip line at 540- 231-6411.

Police flooded the campus, and a composite drawing of a boyish-looking man with spiky, light-colored hair was generated. By midday, officials had canceled all summer school classes for the day and had asked that people stay away from campus.

But four hours after the initial sighting, police had not found a gunman. Police said no other witnesses came forward to say they had seen him.

Campus Police Chief Wendell Flinchum said in an afternoon statement: “We have interviewed several persons similar in description to that provided by witnesses this morning. None of those subjects are the person described.”

Police had questioned the three campers further and deemed their information credible, Flinchum said. “The officers interviewed them, and the information they gave was very detailed,” he said. “The description of what they saw, the officers believed them, and so we deemed it credible at that point.”

The teenagers were attending a camp sponsored by Higher Achievement, a District-based academic organization serving middle school students from underserved areas.

“Higher Achievement can confirm that our scholars were on campus during the situation at Virginia Tech and that three of our scholars reported seeing the suspect,” the organization said in an e-mailed statement.

The three girls were on their way to get food at Dietrick Hall when they spotted the possible gunman, officials said. The campers told a teacher, who informed school security, the statement said.

Officials said the alerts went out about 30 minutes after the first report.

Larry Hincker, a university spokesman, said: “We really need to communicate first and investigate later, and that’s what we did.”

Virginia Tech revamped its alert system after the 2007 shootings. A university official said Thursday that more than 48,000 students and campus personnel received a text message alert and that an e-mail alert was sent to every student and school employee.

“We’re in a new era,” Hincker said. “Obviously the campus went through something terrible four years ago, and the choice facing us, and particularly the police departments, is when you get a report, what are you going to do with the report, regardless of what the veracity may be or the ultimate conclusion might be.”

Ruane reported from Washington. Staff writer Justin Jouvenal contributed to this report.