Anger mounted on Tuesday among survivors of the deadliest shooting rampage in US history over why officials at a Virginia university failed to close the campus when gunfire first broke out.
A total of 33 people died in two incidents at Virginia Tech University on Monday -- almost eight years to the day since 15 people died in the Columbine High School massacre.
An early morning shooting inside a dormitory killed two people and a rampage in another building two hours later left another 31 dead, including the gunman.
As gunshots and screams first rang across the campus, some panicked students leapt from windows and others feigned death to escape the shooter before he eventually turned the gun on himself.
Yet key questions about the crime remained unanswered, including the identity of the gunman, what motivated him, and whether or not he acted alone.
It was also unclear whether two incidents were connected.
"We are working very, very hard to determine if these two incidents are related," campus police chief Wendell Flinchum told reporters.
Relatives and friends of the victims demanded to know why campus officials did not shut down the school after the first incident.
"There was a long lapse between the first incident and the second where 31 people, including the gunman, died and I can't really understand," said student John Reaves, 22.
Flags were to hang at half-mast across the state of Virginia and more details of the crime were expected to emerge at a news conference at 9:00 am (1300 GMT).
On Monday, a visibly shaken campus police chief told of a crime scene that stretched across multiple locations, and said the first shooting had appeared to be "domestic in nature" so authorities did not close the whole school.
The shooter, described by students as "Asian-looking" and wearing a brown hiking shirt and black combat-style vest, carried no identification on him. Police had not yet publicly identified him by early on Tuesday.
Student Erin Sheehan survived along with a handful of classmates in a 20-plus member German class after the gunman barged in twice and fired repeatedly.
"He seemed very thorough about it, getting almost everyone down. I was trying to act dead," she said. "He left for about 30 seconds, came back in, did almost exactly the same thing. I guess he heard us still talking."
Police said they had no suspects in custody but had interviewed a "person of interest."
One of the victims was identified as Ryan Clark, a young man who was shot in the dormitory in the morning. A woman was also killed in that incident, but her name was not released.
After the second shooting began, police had rushed to Norris Hall where they "found the front doors barricaded, chained shut from the inside," said university president Charles Steger.
Police broke into the building and heard gunshots on the second floor.
"Just as officers reached the second floor the gunshots stopped," Steger said.
Two weapons were recovered, and ballistics examination would reveal whether the two shootings were connected, police said.
CNN news citing a source close to the investigation said a .22-caliber handgun and a nine-millimeter handgun were recovered at the scene.
US President George W Bush lamented the loss of life at the university some 425 kilometers (264 miles) southwest of Washington.
"Schools should be places of safety and sanctuary and learning," he told reporters. "When that sanctuary is violated, the impact is felt in every American classroom and every American community."
Virginia Tech, located amid rolling hills in the Blue Ridge mountains, canceled classes and locked down the sprawling engineering and research university which has some 26,000 students and 10,000 staff.
The carnage surpassed the 15 who died in the April 20, 1999 shooting at Columbine High School in Colorado that shocked the nation and the world.
The shooting immediately renewed concern over school security and access to guns that was rekindled last year by a rash of shootings. The state of Virginia has some of the weakest gun licensing requirements in the country, the New York Times said in a Tuesday editorial.
It saw in the carnage "another horrifying reminder that some of the gravest dangers Americans face come from killers at home armed with guns that are frighteningly easy to obtain."