The books I have read on Columbine is as follows(and in no particular order).
Jeff Kass- Columbine: A true Crime Story
Brooks Brown- No Easy Answers
Sue Klebold- A Mother's Reckoning
Dave Cullen- Columbine
Ralph W. Larkin- Comprehending Columbine
I am waiting for the day I can add Randy Brown's book to my list!
But if what you are talking about isn't in these, then maybe it was indeed in a news article/report or some other book that I haven't read.
Hope you find it!