Here's a link to a lot of information about the Columbine attack, in video form (with documentation):
Evan Long - "The Columbine Cause"
Copy for the video:
Evan Long - "The Columbine Cause: An Examination of the April 20, 1999 Attack on Columbine High School" 88 minutes, color.
How many shots? How many shooters? Was it really a surprise?
Many witnesses to the attack reported other Columbine High School students in the trench coat group with Harris and Klebold as shooters. They even named them: Chris Morris, Robert Perry and others. Several named an adult as a shooter in the science halls while police mysteriously waited for hours to enter the school.
Based on the now-public domain government files related to the official "investigation" of the crime.