11:14-11:17 a.m. — Eric Harris and Dylan Klebold carry bombs into the school and plant them in the cafeteria.

11:17 a.m. — The cafeteria bomb, set to go off at this time, fails.

11:19 a.m. — With a shout of "Go! Go!" Klebold and Harris start shooting from the top of the stairs leading into the west side of the school.

11:21 a.m. — Report comes in to Jefferson County dispatch of an explosion in a field at Elmhurst Drive and Wadsworth Boulevard. The bomb was placed there by Harris and Klebold in the hope it would divert authorities there and away from the school.

11:23 a.m. — The first 911 call comes into sheriff's dispatch from the school.

11:24 a.m. — School resource officer Neal Gardner responds to a report of trouble and later trades gunshots with Harris.

11:25 a.m. — First police car pulls up to school, driven by Jefferson County sheriff's Deputy Scott Taborsky. He is followed on foot by officer Paul Smoker.

11:27 a.m. — A pipe bomb goes off in the cafeteria, scattering students and sending smoke billowing through the room.

11:27 a.m. — Harris and Klebold enter the library.

11:30 a.m. — Officers block access to Columbine campus.

11:34 a.m. — The gunmen fire the last shot that kills a victim.

11:36 a.m. — Harris and Klebold leave the library.

11:44 a.m. — Harris and Klebold go to the cafeteria and shoot at their large bombs but fail to set them off.

11:45 a.m. — Harris stops momentarily in the cafeteria to take a sip from a left-behind drink in a Styrofoam cup. They later leave the cafeteria and go to the administration area.

11:46 a.m. — Ten police officers put together a makeshift SWAT team and, using a firetruck as cover, attempt to enter the school.

11:47 a.m. — Another pipe bomb goes off in the cafeteria.

11:56 a.m. — Harris and Klebold, still carrying guns, re-enter the cafeteria.

Noon — Harris and Klebold leave the cafeteria and later return to the library, where they commit suicide.

12:06 p.m. — A second makeshift SWAT team enters the school.

2:38 p.m. — Patrick Ireland slides head-first through the second-story window of the library and is caught by two Lakewood SWAT officers standing on the roof of an armored truck.

4 p.m. — Sheriff's spokesman Steve Davis announces the two gunmen have been found dead of apparent suicide.

4:45 p.m. — Sheriff John Stone arrives at Leawood Elementary School to advise parents that no other survivors remain in school.

April 20, 1999 Eric Harris and Dylan Klebold kill 12 students and a teacher, and wound more than 20 other people before taking their own lives during a rampage at Columbine High School.

October 19, 1999 A 17-year-old Columbine High student threatens to "finish the job" that Eric Harris and Dylan Klebold began. He later is given a one-year deferred sentence after pleading guilty to two misdemeanors.

October 20, 1999 Six month anniversary of Columbine High school shooting. One quarter of Columbine's 2,000 students missed the start of the school day, and another quarter left early.

October 22, 1999 Carla Hochhalter, whose 17-year-old daughter was paralyzed in the Columbine High School shootings six months ago, kills herself inside a pawnshop using one of the store's guns.

December 13, 1999 Families of Columbine victims are allowed to view the contents of videotapes Harris and Klebold made in the weeks before they attacked the school.

December 16, 1999 Michael Ian Campbell, 18, of Cape Coral, Fla., threatens Columbine High School and Columbine student Erin Walton online. The school cancels finals and starts winter break two days early.

February 1, 2000 The body of 11-year-old Antonio Davalos was found stuffed in a trash bin within a mile of Columbine High School. Columbine students sent a large gold ribbon to Davalos' school.

February 14, 2000 Columbine High School students Nicholas Kunselman and Stephanie Hart are found dead at a Subway sandwich shop about two blocks south of the school.

May 5, 2000 Junior Greg Barnes hangs himself in his family home. He leaves no suicide note, but it is believed he hung himself over a breakup with his girlfriend. He did see Dave Sanders get shot on April 20th, and one of his best friends was Matt Kechter.

December 11, 2004 Lance Cpl. Greg Rund is killed in Iraq. He was part of the class of 2002.

March 1, 2007 A bomb threat is called into Columbine High School. The school is evacuated and students sent home for the day. Classes resume the next day.

April 16, 2007 Seung-Hui Cho kills 2 classmates at nearby West Ambler Johnson Hall, then kills 30 more and injures 23 at Norris Hall on the campus of Virginia Tech University. A couple of days later, NBC releases pieces of his writings and a video rant he emailed to their NYC office. In this diatribe, he talks about being "martyrs like Eric and Dylan" and cites the Columbine shooting and shooters. The VT shooting becomes the worst shooting on a school campus since Columbine.