Columbine High School was closed Friday, as it had been every April 20 since the 1999 attack in which two students, Eric Harris and Dylan Klebold, killed 12 classmates and a teacher before killing themselves.
Invoking the Columbine tragedy, Gov. Bill Ritter asked state residents to join a bell-ringing and moment of silence for the Virginia Tech victims on Friday.
"We experienced a terrible tragedy at Columbine High School," Ritter said. "The people of Colorado will stand in solemn silence on the anniversary of that dreadful day with the people of Virginia as they grieve."
The trauma of this week's tragedy was shared by Columbine principal Frank DeAngelis.
"Immediately, my thoughts went back to April 20, '99, and vivid memories. It really does. It retraumatizes you," DeAngelis told CBS News correspondent Lee Frank.
But federal Judge Lewis Babcock's decision earlier this month to seal for 20 years the testimony of Harris' and Klebold's parents about the boys' home lives has infuriated some survivors and victims' relatives, who feel the information could help prevent future school rampages.
"I don't think you can stop every crazy person. But some of the things Babcock locked up show what these crazy kids did," said Don Fleming, whose 16-year-old daughter, Kelly, was killed in the attack. "It's no use to anybody if it is locked up."
"If society knew, it could possibly prevent future shootings," Fleming said. "We're finding out that everything that the latest killer did is similar to what Klebold and Harris did."
Cho Seung-Hui, who killed 32 people on the Virginia Tech campus on Monday before taking his own life, called Harris and Klebold "martyrs" in a videotape.
Fearing the effects of both the Virginia Tech tragedy and the Columbine anniversary, some high schools in other parts of the country canceled classes for the day.
Schools in Yuba and Sutter counties in California were closed after a 28-year-old man allegedly threatened a massacre there.
Tenafly, N.J., schools were closed after a bomb threat was found scrawled in pencil on a door in the high school, specify April 20.
"I don't want my kids in school. God forbid it's true," parent Debbie Werner told WCBS-TV.
Not much has changed in the eight years since Columbine, said Tom Mauser, whose son was killed there.
"We still have a lot of angry people. We still have a lot of firearms, and it's been a pretty deadly mix for us," Mauser told Frank.
In his ruling, Babcock cited a need for confidentiality and concerns that releasing the testimony from the Columbine killers' parents could encourage copycat crimes.
Many in this suburb of Denver think the decision was a mistake.
"Are the people of Virginia going to wait 20 years?" said Dawn Anna, whose 18-year-old daughter, Lauren, was killed at Columbine.
For some here, watching events unfold in Virginia was a painful reminder of the chaos and suffering thrust on them eight years ago. The parents of students slain at Columbine met this week to deal with the shock of the Virginia killings. The judge's decision dominated their conversation.
"I felt like I was looking at Lauren's murderer. It's as if someone has been cruelly replaying April 20," Anna said.
The Harrises and Klebolds commented publicly only through their lawyers. Michael Montgomery, an attorney who represented the Harris family, said the judge "made an absolutely appropriate decision." The judge declined to comment Thursday.
Much information about the Columbine killers is available on the Internet, including video clips of the two practicing their marksmanship, Harris' diaries, and Web sites dedicated to both killers.
Authorities learned that Harris and Klebold played violent games, made violent videos at school and were bullied.
Researchers into school-related violence support the Columbine families' position on releasing the tapes, noting the relative frequency of violent campus incidents. The Centers for Disease Control reported in 2002 that were 220 school-related shootings from 1994 to 1999, resulting in 253 deaths.
"The judge said the tapes were incendiary. We have plenty of things already that stimulate violence," said sociologist Ralph Larkin, author of "Comprehending Columbine."
Katherine S. Newman, a professor at Princeton who has written about shooting rampages, said the information should be released.
"A 20-year lag deprives the rest of the country of what might be valuable insight," she said. "Indeed, having done a lot of research with the families of victims, they are left with a big hole in the middle not only by the loss of their children but by the unanswered 'why' questions."