Violence returned to Virginia Tech, the scene in 2007 of the deadliest school shooting in US history, when two people were shot dead including a campus police officer. Police refused to confirm reports that the second fatality might have been the shooter himself, even as the 31,000-student university lifted an afternoon-long lockdown and declared there was no longer an "active threat." But when asked if the gunman was at large, Virginia State Police spokesman Bob Carpentieri cryptically told reporters: "Investigators feel confident that they have located the person." The slain police officer, a four-year veteran of Virginia Tech's own security force, was shot and killed during a noon-hour "routine traffic stop" in a parking lot near a sports facility. "Witnesses reported to police the shooter fled on foot heading toward the Cage, a parking lot near Duck Pond Drive," the university said in a statement on its website (www.vt.edu). "At that parking lot, a second person was found. That person is also deceased." No names were disclosed, but Carpentieri said a weapon was found close to the second victim, who he described as a white male. He also said the gunman was not the motorist who the slain police officer had pulled over. Virginia Tech was the scene of the deadliest shooting incident by a single gunman in US history in April 2007 when an English major, Seung-Hui Cho, 23, killed 32 people before taking his own life. Twenty-five others were wounded. "It brings back difficult memories from the past," Virginia Tech president Charles Steger told reporters. Thursday was a study day on the eve of final exams for the fall term, which have been pushed back a day until Saturday. Ironically, Virginia Tech officials -- including the campus police chief -- were in Washington on Thursday to appeal a $55,000 fine for failing to promptly issue an email alert after Cho shot his first two victims in a dormitory. One unidentified student, fighting back tears, told local WDBJ television she witnessed the fatally wounded police officer fall out of his unmarked vehicle when colleagues opened its door. "He just fell out towards the ground, and then they immediately started reviving him, and then two cops took off with some sort of automatic weapons, I guess, running in the opposite direction after the gunman," she said. "I guess the officer didn't make it because they just covered him with a sheet." The gunman was described as a white male in a maroon hooded sweatshirt and grey sweatpants. Maroon is the official color of Virginia Tech. Police with handguns drawn and assault rifles at the ready swarmed across the campus as students and staff took refuge for four hours in their dormitories, offices and a leisure center. Virginia Tech employee Brian Walls told CNN he initially heard 10 to 15 different sirens wail, and then went outdoors where he witnessed a large group of police officers. "I ended up seeing an individual on the ground" and rescue workers apparently trying to revive a fallen person, he said. "Then the campus alarm alerts went off" and Walls got back inside. Tauhid Chappell, a student, said he and other students were getting information through the university's multi-tiered alert system -- put in place after the 2007 bloodbath -- as well as the Internet and radio. The atmosphere on campus felt "very quiet and still," he told CNN. "I was in my dorm all day and I saw just a bunch of action on campus," first-year student Andrew McElvarr told WDBJ television. "Everyone (in the dormitory) is just waiting, watching, trying to figure out what's happening." Virginia Governor Bob McDonnell said: "Virginia Tech is a university of great resolve, and I have no doubt that the students, alumni and faculty of this proud institution will emerge from this sad day stronger and more united than ever before."