Red Flags?

Could one of the most horrific episodes of in-school violence have been prevented? In hindsight, there were many clues that pointed to the plot of teens Eric Harris and Dylan Klebold.
Feb. 15, 1998
Jefferson County Sheriff's deputies respond to a report of a pipe bomb in a field. They find and defuse a 6- to 8-inch-long PVC pipe packed with fireworks powder, according to an affidavit. Police later suspect that this bomb was set off by Eric Harris and Dylan Klebold.
March 25, 1998
Harris and fellow gunman Dylan Klebold plead guilty to first-degree criminal trespass and theft, for breaking into a van and stealing tools. They are placed in a juvenile-diversion program and complete it in February 1999.
March 1998
AP Photo
After having found a death threat against their son on Eric Harris's Web site, Randy and Judy Brown take pages from the site to the Jefferson County Sheriff's Office. A sheriff's investigator tells them that Harris already has a criminal file, from the van break-in.
April 1998
Police paperwork shows that investigators were preparing an application for a warrant to search Eric Harris's home. One document shows that a sheriff's deputy found an unexploded pipe bomb "consistent with the devices" Harris said on his Web site that he had exploded. But the sheriff's department never obtained a warrant and so never searched, or even visited, the Harris home.
April 1998
After meeting with the Browns, sheriff's deputies warn Columbine administrators that Harris might be making bombs. According to Sally Blanchard, a school district official: "They were told that it didn't involve the school and they should take no action." The Sheriff's department denies that its deputy told the school not to look into the matter.
Aug. 1998
Joe Schallmoser and Howard Cornell, who are in charge of security for the school district that includes Columbine, write a security plan requiring school officials to notify and meet with parents and law enforcement officers as soon as they learn of any student threats of violence. They say now that Columbine didn't follow the plan.
Dec. 1998
Columbine student Devon Adams also finds her name on Harris' web site - on his hit list. According to Adams, she tells an assistant principal at Columbine about the threat, but now the assistant principal denies having the conversation. By then Klebold and Harris have already bought a rifle, a semiautomatic pistol and two sawed-off shotguns.
March 1999
Harris and Klebold practice shooting at trees and bowling pins six weeks before their suicidal rampage, as revealed in a self-made videotape that police released to the public in 2003.
April 20, 1999
AP Photo
Harris and Klebold go on a carefully planned rampage at Columbine, killing 13 people and wounding 23 more before taking their own lives.
Feb. 26, 2004
A report reveals authorities had at least 15 contacts with the gunmen dating back two years before their murderous attack, ranging from complaints about snowballs to tips about bomb boasts and death threats on Harris' Web site.
July 6, 2006
Hundreds of pages of hate-filled diary entries, maps and documents that offer a chilling insight into the minds of the killers in the days and months before the 1999 massacre are released.