DENVER -- The suspect in one of the deadliest school shootings in American history had a history of violent posts, including a YouTube comment about wanting to become a "professional school shooter."
The missed warning signs are sparking conversations in Colorado about sounding the alarm.
On Thursday night, Colorado State University police asked students on Twitter to "Speak up when a friend needs help," suggesting they look for changes in behavior, weigh, hygiene and motivation. It also says the school offers confidential services.
Meanwhile, the principal at Harrison High School in Colorado Springs announced Thursday the school is postponing Friday's pep assembly because of chatter about "possible acts of violence."
In Colorado, the Safe2Tell program, through which people can anonymously report concerns, has seen a significant increase in reports. In January alone, Safe2Tell had 1,321 reports, a 68 percent increase from 2017, ranging from suicide threats to planned school attacks.
Colorado's Attorney General, Cynthia Coffman, said Safe2Tell has prevented numerous acts of violence in Colorado schools and saved lives.
"What I think is most important is kids trust their gut instincts because we know when something doesn't seem right," said Coffman.
If you think there's suspicious activity around you, make a report using your smartphone by downloading the Safe2Tell Colorado mobile app from the Apple Store or Google Play or by calling 1-877-542-7233 to speak to a live, trained dispatcher.