The book itself is one of the most recent books published on this particular subject and as a result, the author, Dave Cullen is able to draw upon a large range of sources, from eye-witness accounts recorded at the time of the massacre, journals and videos released by the killers through to police and court reports released many years later.
If you have read anything about this subject in the past and want to read this book, the first thing I would suggest is that you forget all the 'accepted facts' you have read so far, 'facts' such as the boys were part of the Trenchcoat Mafia, that the boys carried out the killings due to school bullying, that the boys were fans of Marilyn Manson or that they set out to target the school 'Jocks' - all these 'facts', according to all the sources referenced in this book are inaccurate or false.
The argument put forward initially for these inaccuracies come from the initial reports which were recorded by the media as the massacre was unfolding. Many of these 'facts' were taken directly from school kids as they escaped Columbine High, which when you think about it is not the best time to try to get information from people who have been through such an incident, as they would be going through any number of emotions at that time.
A number of reviews of this book criticized it because it was constantly jumping back and forward throughout the timeline of events, personally I felt this worked very well as it allowed for you to build up a picture of what happened, then to find out the background as to why it happened then the aftermath of that particular event. Quite surprisingly one of the last things to be discussed in this book was how the killers met their deaths, it was quite a poignant moment.
On of the strongest feelings that you get from reading this book is that if things had been different and some of the key 'events' leading up to the massacre had been picked up on by either the police, teachers, family or friends, there is no doubt in my mind that Dylan would not have taken part in the shootings of April 20th 1999, as its clear that he was not the psychopath he was portrayed as, yes, he was a very depressed teenager with strong thoughts of suicide, but in the early stages he just wanted to end his own life, not that of himself and as many other people as possible.
Eric was the polar opposite, he was a text book psychopath who took Dylan's thoughts and molded him into the killer he became. Eric's main aim was to take down as many people as possible, not just as many hundreds of students as possible, but also as many of the emergency service people and parents who attended the incident.
This would have happened if Eric's bombs had detonated as he had hoped, the number of fatalities would have been in the hundreds, rather than teens.
If you have an interest in the area of True Crime I would strongly suggest you take a look at this book as it really is a fascinating read.
The book is accompanied by a very detailed Online Resource which goes into a lot more detail about many aspects which are covered in the book, but not in thorough detail (if they had been, the book would have been thousands of pages long and not at all easy to read.)
A link to the Amazon page for this book can be found HERE