Alan Kim | The Roanoke Times

Blacksburg and Virginia Tech Police Department officers were among area law enforcement agents who responded Thursday afternoon to a report of gunshots at Pritchard Hall. The sound turned out to have been created by a nail gun cartridge.

Virginia Tech police Chief Wendell Flinchum leaves after completing the initial investigation at Pritchard Hall.

Residents and onlookers wait outside Virginia Tech's Pritchard Hall (located at left, not visible in photo) after university police closed the dormitory Thursday as a result of hearing reports of gunshots in the area. It was later determined that the sounds had been caused by a nail gun cartridge, not by gunshots.

BLACKSBURG -- Reports of gunshots fired Thursday at Virginia Tech led to multiple campuswide alerts and a two-hour closing of a residence hall before police determined the sound was caused by a nail gun cartridge.

The day's events were an uneasy reminder of shootings on campus a year and a half ago and exposed a problem with some of the emergency notification systems implemented after the tragedy.

About 12:43 p.m., students in Pritchard Hall -- a 1,000-student, all-male residence -- reported hearing sounds they believed to be gunshots.

Virginia Tech police secured the building and conducted a room-to-room search and interviewed witnesses who reported seeing two people next to a trash container outside the building at the time of the explosion. Students were allowed to leave the building but were asked for their student identification numbers before exiting.

Police stood guard at each of the building's entrances and did not let anyone in until about 2:50 p.m., when they determined that no shots had been fired. Law enforcement personnel from Blacksburg, Montgomery County, Dublin and from state police also responded to the incident.

The university administration, which has added several security measures since the April 16, 2007, shootings, sent out alerts via e-mail at 1:41 p.m. The university Web site and electronic message boards installed in classrooms this summer also reported that witnesses had heard gunshots in Pritchard.

The initial alert said the building had been secured and there was no odor of gunpowder in Pritchard. It also suggested the sound may have come from construction across the street from the building.

The university sent two more alerts at 2:31 and 2:55 to announce that the sound may have come from students exploding firecrackers near the trash bin, and to announce the end of the threat.

Tech spokesman Larry Hincker said the situation highlighted some of the problems of immediate notification when the details of a developing situation are uncertain.

Several students complained that they did not receive text message alerts about the incident and Hincker said there was a problem with the alert system, which the university implemented in the fall of 2007.

The initial alert only reached some text and voice mail subscribers and the two alerts that followed did not reach any phones and nonuniversity e-mail accounts, which are also controlled by the text alert system provider -- California-based 3n, National Notification Network.

Hincker said the university contacted 3n Thursday afternoon but the company did not know what went wrong.

"Frankly, we're not happy," he said.

Police cars and yellow caution tape surrounded the building Thursday afternoon as police walked bomb-sniffing dogs in the area.

Students, reporters and onlookers lined the sidewalks around the building as police searched it. Some students talked on their cellphones, trying to get details about what had happened.

Hincker acknowledged that the scene was unsettling to some who experienced the April 16 shootings, when many students mistook what was actually gunfire for construction noise.

"Our university community, obviously, is on edge right now because of what was reported," Hincker said. "Anybody who has been on this campus the last year and a half is going to be on edge and I would not blame them. Certainly I was."

Boomer, the Tech police department's new explosive-detection dog, found the exploded cartridge from the powder-actuated nail gun near trash bins between Pritchard and Lee Hall, said Tech police Assistant Chief Tom Foster.

Foster said students and employees reported seeing two young men near the containers at the time of the explosion. The noise may have bounced off the buildings creating the impression of multiple shots, he said.

Witnesses described seeing one white man wearing a hooded gray sweat shirt and one black man with a bushy or braided hairstyle near the trash bins and said they smiled and laughed after the explosion, which they may have created by slamming the lid on the cartridge.

Police had not found them as of Thursday evening.

When asked if they could be charged with a crime for exploding the cartridge, Foster said it would depend on the circumstances and "would be something, really, for the commonwealth's attorney to determine."

Pritchard resident Robin De Leon, 18, of Virginia Beach heard about the reported gunfire as he rode a Blacksburg Transit bus back from Kroger.

Standing on the sidewalk in front of the dorm with a case of bottled water, De Leon said it was weird seeing all the police cars and crime scene tape around the building.

"It's kind of freaky, especially after the whole incident of the shootings just last year," De Leon said.

Staff writer Shawna Morrison contributed to this story.