Blacksburg, Va. ? A gunman walked into a parking lot and killed a Virginia Tech police officer who was conducting a traffic stop on campus Thursday, state police said.

Sgt. Robert Carpentieri said it appeared that the shooter was not in the car that had been pulled over. The sergeant said another officer later spotted a second person in a different parking lot who was alive at the time. That person, a white man, later died of a gunshot wound.

Police would not say during a Thursday afternoon news conference whether the second dead person was the gunman who killed the officer. However, a law enforcement official who had knowledge of the case and spoke on condition of anonymity told The Associated Press that the gunman was believed to be dead.

Virginia Tech officials said on the school’s website that a weapon was recovered near the second body found on campus. School officials also said there was no longer an active threat Thursday afternoon and that normal activities could resume.

Investigators were interviewing the person who was pulled over Thursday. Carpentieri also said he couldn’t say exactly how many people were involved.

The officer had served on the campus police force for four years. State police were still investigating whether he had been specifically targeted.

The officer’s shooting prompted a lockdown that lasted for hours.

As police hunted for the killer, the school applied the lessons learned nearly five years ago, warning students and faculty members via email and text message to stay indoors. It was the first gunfire on campus since 33 people were killed in the deadliest mass shooting in modern U.S. history.

The shooting Thursday sent a shudder through campus, where students preparing for exams were suddenly told to hunker down. Heavily armed officers walked around campus as caravans of SWAT vehicles and other police cars with emergency lights flashing patrolled nearby.

“A lot of people, especially toward the beginning were scared,” said Jared Brumfield, a 19-year-old freshman from Culpeper, Va., who was locked in the Squires Student Center since around 1:30 p.m. “A lot of people are loosening up now. I guess we’re just waiting it out, waiting for it to be over.”

The university sent updates about every 30 minutes, regardless of whether they had any new information, school spokesman Mark Owczarski said.

“It’s crazy that someone would go and do something like that with all the stuff that happened in 2007,” said Corey Smith, a 19-year-old sophomore from Mechanicsville, Va., who was headed to a dining hall near the site of one of the shootings.

He told The Associated Press that he stayed inside after seeing the alerts from the school. “It’s just weird to think about why someone would do something like this when the school’s had so many problems,” Smith said.

Harry White, 20, a junior physics major, said he was in line for a sandwich at a restaurant in a campus building when he received the text message alert.

White said he didn’t panic, thinking instead about a false alarm about a possible gunman that locked down the campus in August. White used an indoor walkway to go to a computer lab in an adjacent building, where he checked news reports.

“I decided to just check to see how serious it was. I saw it’s actually someone shooting someone, not something false, something that looks like a gun,” White said.

Campus was quieter than usual because classes ended Wednesday and students were preparing for exams, which were to begin Friday. The school postponed those tests.

The shooting came soon after the conclusion of a hearing where Virginia Tech was appealing a $55,000 fine by the U.S. Education Department in connection with the university’s response to the 2007 rampage.

The department said the school violated the law by waiting more than two hours after two students were shot to death in their dorm before sending an email warning. By then, student gunman Seung-Hui Cho was chaining the doors to a classroom building where he killed 30 more people and then himself.

The department said the email was too vague because it mentioned only a “shooting incident,” not the deaths. During testimony Thursday, the university’s police chief, Wendell Flinchum, said there were no immediate signs in the dorm to indicate a threat to the campus. He said the shootings were believed to be an isolated domestic incident and that the shooter had fled.

An administrative judge ended the hearing by asking each side to submit a brief by the end of January. It is unclear when he will rule.

Since the massacre, the school expanded its emergency notification systems. Alerts now go out by electronic message boards in classrooms, by text messages and other methods. Other colleges and universities have put in place similar systems.

Universities are required under the Clery Act to provide warnings in a timely manner and to report the number of crimes on campus.

During about a one-hour period on Thursday, the university issued four separate alerts.

Derek O’Dell, a third-year veterinary student at Virginia Tech who was wounded in the 2007 shooting, was shaken.

“It just brings up a lot of bad feelings, bad memories,” O’Dell said. “You pray there are no more victims, and pray for the families.”

O’Dell was monitoring the situation from his home a couple of miles from campus.

“At first I was just hoping it was a false alarm,” he said. “Then there were reports of two people dead, and the second person shot was in the parking lot where I usually park to go to school so it was kind of surreal.”

In August, a report of a possible gunman at Virginia Tech set off the longest, most extensive lockdown and search on campus since 2007. No gunman was found, and the school gave the all-clear about five hours after sirens began wailing and students and staff members started receiving warnings.

The system was also put to the test in 2008, when an exploding nail gun cartridge was mistaken for gunfire. Only one dorm was locked down during that emergency, and it reopened two hours later.

Tucker reported from Washington. Associated Press writers Kimberly Hefling and Ben Nuckols in Washington and Michael Felberbaum and Larry O’Dell in Richmond, Va., contributed to this report.