Key organisational failures that left Virginia Tech student Seung-hui Cho free to kill 32 people should never be repeated, Virginia's governor has said.
The gunman, Seung-hui Cho, was a student at the university
Tim Kaine lamented a series of "missed opportunities" that allowed Cho to remain at large despite serious concerns over his mental health.
He spoke at the launch of a report that was critical of the emergency response to Cho's April rampage.
It says that lives may have been saved if college officials had acted sooner.
"Warning students, faculty and staff might have made a difference," the report says.
However, it did concede that while a lockdown might have helped protect some students and teachers it would probably have been ineffective in stopping Cho, who "had started on a mission of fulfilling a fantasy of revenge".
The independent eight-member panel also concluded that though Cho had shown earlier signs of mental instability, college staff had not intervened effectively.
Cho killed 32 people and himself at the US university in April in the deadliest shooting spree in modern US history.
The president of Virginia Tech, Dr Charles Steger, said the report's findings were "painful" but "necessary". He said the college needed to be more aggressive in identifying students at risk and would be expanding its capacity to care for them.
But he staunchly defended the police response, saying that the notion of a two-hour gap in dealing with the emergency was a "great misconception".
Dr Steger also said families should not surrender responsibility for students, and that no-one at the college had been made aware of Cho's prior mental health problems.
Mr Kaine, who commissioned the report, said a combination of poor college administration, inadequate mental health services and policing errors allowed Cho to live among the students he would eventually attack.
He expressed concern that other students with potentially dangerous mental health issues were living unmonitored on college campuses across the US.
Describing Cho as "fixated" with violence, Mr Kaine said no record of the student's troubled personal history ever reached Virginia Tech authorities.
During the time Cho was at Virginia Tech a number of students had "interactions with him that were clearly indications he was troubled and needed assistance", Mr Kaine said.
But, he added, no mechanism existed to deal with Cho's problems on campus.
Mr Kaine also pointed to failures in the information flow within the mental health system, where Cho was once referred by court order.
Police were aware that Cho, who moved to the US with his family from South Korea in 1992, had been admitted to a mental health unit in late 2005.
He was sent for evaluation after two female students made complaints against him, following a period of bizarre behaviour and concerns that he was suicidal.
But the information was never passed on to university officials because of a lack of resources, misinterpretation of privacy laws and passivity, the report said.
The panel also said officials should have issued an alert or cancelled classes after Cho shot his first two victims - Emily Hilscher and Ryan Clark - in a dormitory just after 0700 on 16 April.
The 27 dead students were awarded posthumous degrees
But Mr Kaine said campus police did not have adequate authority to take firm, quick action.
More than two hours later Cho killed 30 students and teachers, plus himself, at the Norris Hall complex in another area of the campus.
At 0926 the university sent an e-mail to students and staff warning of a "shooting on campus" and urging caution.
"There does not seem to be a plausible scenario of a university response to the double homicide that could have prevented the tragedy of considerable magnitude on April 16," the report said.
"There was much in the emergency response that was heroic. But there were also instances... that led to frustration," Mr Kaine said.
"What we have to do now is to challenge ourselves to study this report carefully, to make changes that will reduce the risk of future violence."