The department issued its report in January, but it gave Virginia Tech a chance to comment before drafting the final version, which was issued Thursday.
The report finds that the university failed to issue a timely warning after the gunman killed two students in a dormitory early on April 17, 2007.
The school sent out an e-mail about the shootings two hours later, but by that time, the student gunman was chaining shut doors to a campus building, where he killed 30 students and faculty before turning the gun on himself.
A university spokesman disputed the findings.
The Virginia Tech shooting rampage is the deadliest peacetime shooting incident by a single gunman in U.S. history.
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