Asked if police were still looking for the shooter, state police Sgt. Robert Carpentieri said: "I think the investigators feel confident that we've located the person. I can't give you specifics and I don't want to confirm that but you can kind of read between the lines so I won't specifically address that question."
The campus police department has about 50 officers and 20 full- and part-time security guards.
Many students were preparing for exams when they were suddenly directed to hunker down. Heavily armed officers swarmed the 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.
The university sent updates about every 30 minutes, regardless of whether they had any new information, school spokesman Mark Owczarski 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.
The campus was quieter than usual because classes ended Wednesday. About 20,000 of the university's 30,000 students were on campus when the officer was shot. Exams, set to begin Friday, were postponed.
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 federal agency said the university 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 has 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.
Andrew Goddard, who has crusaded for stiffer gun control laws since his son Colin was wounded in the 2007 shootings, said Virginia Tech's response seemed much better this time.
"It sounds like things moved very, very fast this time as opposed to the time before," said Goddard, who has a daughter and nephew that go to the school. "That doesn't surprise me. Virginia Tech really did get the message in the sense that when bad things are happening, you have to ask quickly."
Monica Borza, a senior majoring in biological studies from Virginia Beach, said in an email to the Associated Press that she chose to attend Virginia Tech because she thought she would be able to feel safe there.
"The dedication of the officers today confirmed my decision," said Borza, who was at the Blacksburg public library when she got a text alert about the shooting.
"Within minutes, all my friends and family checked in with me to make sure that I was safe," she said. "For the next couple of hours, my phone was constantly going off with text messages and phone calls saying, 'Are you okay?' 'Praying for VT!'"