Foreword

On a sunny spring day in April 1999, a suburban high school in Jefferson County, Colorado, found itself under attack by two of its own. In less than fifteen minutes of the first-lunch period on that Tuesday, two student gunmen killed 13 and wounded 21 before they turned the guns on themselves - the most devastating school shooting in U.S. history.

Columbine High School is one of three in the unincorporated southeast portion of Jefferson County. The county itself lies on the west side of the Denver metropolitan area and is the most populated county in the state. The large unincorporated region along the county's southern plains and foothills has a population of nearly 100,000 residents - 1,945 of who attended Columbine High School.

The two student gunmen were Eric Harris and Dylan Klebold. Their plans for attacking the school, recovered by investigators after the tragedy had taken place, evolved over one year's time. In those plans, Klebold and Harris outlined a mission to kill as many students and faculty as possible. They would set off destructive bombs inside the school and then shoot any survivors trying to run out. Bombs inside their cars would explode later, killing law enforcement, fire or medical personnel responding to the scene.

There are indications that their initial plan was for the Columbine High School attack to occur on Monday, April 19. While there was no specific reference made in their writings to this date being an important anniversary, it must be noted that April 19, 1999 was the fourth anniversary of the bombing of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma and the sixth anniversary of the Branch Davidian standoff in Waco, Texas.

However, the Columbine tragedy occurred on April 20, perhaps due to unfinished preparations on the part of the killers. Or perhaps there is a connection with the history of this date. Due to the significance of these numbers in popular drug culture, some students were absent from school that day in recognition of what they termed "national marijuana day." April 20, 1999, also marked the 110th anniversary of Adolph Hitler's birth.

It is also critical to note that when many of the Columbine students heard what sounded like pop guns coming from outside the cafeteria during the first lunch period, they thought that senior prank day had come. School-wide pranks initiated by graduating seniors aretradition throughout the United States, and up to that point Columbine's seniors, ready to graduate in just four weeks, had not participated in any such activity. It seemed right to students who heard the first few shots that, as it was toward the end of the school year, prank day was finally upon them.

But it wasn't a prank. Not when two hate-filled students, heavily armed with firearms and bombs, chose April 20, 1999, as the day to attack and kill students and faculty at their school.

THE SHOOTINGS

During the investigation of this case, several sources were utilized in compiling an accurate chronological timeline of the many different events that occurred at Columbine High School on April 20, 1999. This included dispatch and 911 tapes from the Jefferson County Sheriff's Office, dispatch tapes from the Littleton Fire Department, several newscasts from local media, the record of the school fire alarm system and the cafeteria surveillance videotape from Columbine High School.

Two weeks of the investigation, investigators learned that the Jefferson County Sheriff's Office had recently calibrated its digital clocks used for dispatch tapes with the National Institute of Standards and Technology (NIST) atomic clock in Boulder, Colorado. Therefore, the Jefferson County Sheriff's Office dispatch time was the standard used for the timeline. It was further learned that the Sheriff's Office 911 times had not yet been calibrated and were fast by two minutes and 46 seconds. The Littleton Fire Department dispatch time was four minutes slow and the fire alarm from Columbine High School was three minutes slow. The times on the cafeteria videotape matched the Sheriff's Office dispatch time.

In order to accurately reflect the events occurring on April 20, it became necessary to adjust the times so that they were synchronized to one time -- in this case, the Jefferson County Sheriff's Office dispatch time. The following changes were made and are reflected in the finished timeline:

• 4 minutes were added to the Littleton Fire Department dispatch time
• 3 minutes were added to the school fire alarm time
• 2 minutes 46 seconds were subtracted from the Jefferson County 911 time
• No adjustments were made to the high school cafeteria surveillance tape.