There have been several excellent reports. Most of what you're searching for is probably already gathered up here.

On School Shooters

These reports are incredible. They were created by some of the best minds in the field, and their research was exhaustive and impecible. It's a crime how few people know about them. All the myths about school shooters are cleared up here. (Eg, most are not loners or outcasts, they rarely "snap," and their is no accurate"profile.")

They are all written for general readers, and are easy to digest. No scholarly fox index here. I recommend them all, but placed them in priority order.

1. The Final Report and Findings of the Safe School Initiative: Implications for the Prevention of School Attacks in the United States. U.S. Secret Service and U.S. Department of Education. May 2002.

2. FBI Report: The School Shooter: A Threat Assessment Perspective. Federal Bureau of Investigation. U.S. Department of Justice. Critical Incidence Response Group. National Center for the Analysis of Violent Crime. Mary Ellen O'Toole.

3. Centers for Disease Control and Prevention. School-Associated Student Homicides: United States, 1992 - 2006. 57(02);33-36. January 18, 2008.

On Columbine

Jeffco Sheriff's Office Final Report on the Columbine High School Shootings. (Link hosted by Rocky Mountain News.) Jefferson County Sheriff's Office. CD, May 15, 2000.

The report will satisfy most needs. It is exhaustive on most details about the case, and impeccable in general. However, there are some glaring omissions, particularly anything about the killers' motive.

Of course you should disregard this report on anything related to Jeffco's own role in the tragedy, including before, during and after the attack.

One noteworthy mistake is the report mis-identifies the killer of Danny Rohrbough. See the El Paso report below, which supercedes it on anything involving that aspect of the attack.

One big flaw in the report for users is its terrible organization. It runs the equivalent of close to 1,000 pages, but was released straight to DVD, with no "pages" or page numbers. Much important material is buried in odd places. This Reader's Guide to the Columbine Report" is really helpful in sorting through it. It was done by Daryl Lindsey, for Salon, May 17, 2000.

Columbine Review Commission's Report to Governor Bill Owens Hon. William H. Erickson, Chairman. May 2001.

This report was based on an outside investigation, with very useful commentary on Jeffco's role. That will be the chief use of it for most readers. It was not given subpoena power, however, which greatly limitied its ability to perform the intended role. (Its lack of power caused great controversy, which was justified.)

For people digging really deep, it also includes lots of additional details on assorted topics.

Reinvestigation into the Death of Daniel Rohrbough at Columbine High School on April 20, 1990. El Paso County Sheriff's Office, John Wesley Anderson, Sheriff. April 10, 2002.

This investigation/report was in response to great controversy over who killed Danny Rohrbough. They did a very thorough job, and his family fully embraced its findings.