A gunman ambushed and killed a campus police officer and was later reported to have been found dead on Thursday at Virginia Tech University, the site of one of the worst shooting rampages in US history.Authorities declared the campus safe and lifted a lockdown after a nearly four-hour manhunt, seeming to lend credence to television news reports that a body found in a Virginia Tech parking lot was that of the shooter.Police at a televised news conference declined to say whether they suspected a murder-suicide and offered no motive for the crime, citing an ongoing investigation."Today tragedy again struck Virginia Tech with a wanton act of violence where a police officer was murdered during a routine traffic stop," Virginia Tech president Charles Steger told reporters. "Words don't describe our feelings."The incident evoked grim memories of April 2007 when a mentally deranged student killed 32 people and wounded 25 before committing suicide on the school's rural campus in the Shenandoah Valley about 250 miles (400 km) from Washington. It was the deadliest attack by a single gunman in US history.In Thursday's incident, the gunman walked up and shot dead a four-year veteran of the campus police force during a routine traffic stop, police said.The man then fled on foot toward a nearby parking lot, and a body was later found there along with a gun, police said.But Sergeant Bob Carpentieri of the Virginia State Police would not confirm that the second body was that of the unidentified gunman. He said, however, that investigators were looking at the possibility that the shooter was linked to an armed robbery earlier in the day in the nearby town of Radford, Virginia.Police, some in combat gear with assault rifles, swarmed the campus after the shooting, while students and faculty were ordered to hunker down inside university buildings and dormitories.Several hours later, the university declared an end to an "active threat" on campus, telling the college community to "resume normal activities."During the lockdown, parents of students had sought frantically to locate their children by mobile phone and social networking sites."Right now it's kind of scary and hectic around here that this is happening again," Matthew Spencer, a Virginia Tech freshman, told a local NBC station before the all-clear was given.US House of Representatives Republican Leader Eric Cantor of Virginia was among the first members of Congress to weigh in. "Such violence is never easy to explain, and cuts to our core - especially on a campus that has experienced such grief in the past," he said.Virginia Governor Bob McDonnell said: "I am deeply saddened by today's news of another tragedy affecting the Virginia Tech community. Our thoughts and prayers are with the families of those impacted by these shootings." The school, formally known as Virginia Polytechnic Institute and State University, was criticized for its slow response to the 2007 incident and has since put a campus-wide alert system in place.Final exams set to begin on Friday for the fall semester were postponed.Elizabeth Sullivan, a sophomore, said about 200 students were sent to the second floor of the Squires Student Center from the ground floor about an hour after the shooting.Shortly after that, a SWAT team arrived to pat down each student and check every bag in the building."I was pretty nervous at first. I didn't really know what was going on," Sullivan told a local NBC television station.She said most students had been keeping in touch with their families through Facebook and Twitter.The 2007 Virginia Tech massacre renewed a chorus of calls for tougher gun control laws, particularly in the US Congress.But these calls did not get far since Republican lawmakers have traditionally opposed gun control and Democrats, having been burned on the issue politically, did not push it.Since taking office in January 2009, US President Barack Obama has shied away from stiffer gun laws despite demands for it by members of his largely liberal base.