Editor's Note: The following is an expanded version of the interview that was published in the September 2009 issue of POLICE Magazine.

Dave Cullen's "Columbine" is not just a best-selling true crime story. It doesn't just journalistically examine the events of the nation's most infamous school massacre, it brings them to life.

Focusing on 10 characters-including the mass murderers Eric Harris and Dylan Klebold-as well as teachers, parents, cops, victims, and survivors, "Columbine" is a non-fiction novel, a non-fiction horror novel.

The monster in this horror story is 18-year-old Eric Harris. Cullen makes a forceful argument that Harris was a sadistic psychopath who felt absolutely no remorse and acted with no conscience. Even if you don't buy Cullen's hypothesis, it's hard to argue that Harris wasn't a monster.

Although Columbine ended up being the nation's most infamous school shooting, it was planned as a bombing. Harris and his accomplice Dylan Klebold, 17, placed two large propane bombs in their school cafeteria right before the lunch hour rush. Their plan was to wait until the bombs detonated  and then mow down the panicked survivors with a  small arsenal of shotguns and carbines.

Cullen, a freelance writer who lives in Colorado, has been delving into the psyches of Harris and Klebold ever since the day of the attack when he rushed to the scene to cover the breaking story. It's a story that he can't seem to shake because every time a school shooting occurs anywhere in the world, the media contacts him. "It can be a bad way to wake up," he says.

POLICE Magazine editor David Griffith recently spoke with Cullen about the psychology of Eric Harris, law enforcement response the day of the massacre, the investigation, and how school shootings can be prevented.

When did you first get involved with the Columbine story?

Sometime A little before noon that day I saw it come on TV. I didn't know where it was. I drove out Highway 6 until I saw the helicopters circling south from the highway. That was my first clue that it was much worse than I thought. So I just got off at the next exit and drove until I was stopped by a police barricade.

Then I pulled into a strip mall and got out on foot and ran. I got as far as the Columbine Library, which was maybe half a mile from the school. That was one of the two rendezvous points. Most of the scenes in the book of the parents waiting there for word about the fate of their children was from what I noted there that day.

Why do you think Eric Harris decided to murder his classmates? Was it because he hated jocks? Or preps? Or bullies?

With Eric what I always tell people is please avoid cherry-picking the Eric quotes because Eric rants about everything under the sun, including slow drivers. That doesn't mean he shot up his high school because of slow drivers.

But when you look through the hundreds of pages that he left, the patterns leap out at you, and the patterns are really important. One of the patterns is his real desire, which he repeats more than anything else in all of his writing other than perhaps "I hate you all," and that is: "I want to kill you all." His ultimate fantasy was annihilation of the human species.

He couldn't destroy the world, so he settled for his school.

Yes. He complains in his journal about how hard it is to get enough explosives to destroy one building. Then he says, "Bombs are hard." The rational side of Eric realized: Destroying the world is way beyond me. Burning down Denver is way beyond me. Even downtown Denver is way beyond me. But I can take out my high school.

The pattern of terrorists in general is that they usually go for symbols, and they usually go for explosions. They also usually go for symbols of power and authority. Eric and Dylan attacked the biggest power center of their world, which was their school.

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Eric leaked a lot of information about his plans. Why didn't somebody realize that he was a threat?

Eric was so smart about knowing where to stop. You can see that in the school assignment paper that he wrote about the Nazis. He knows in that paper exactly what he's got to say so that the teacher doesn't think, This kid is dangerous. But in his journal, he writes: "I want to do this, too. The Nazis are role models for me. I want to do everything those people did. They had a great plan."

You argue that Dylan Klebold would not have turned homicidal without the psychopathic influence of Eric Harris. Let's flip that for a moment. Do you think that Harris would have attacked his schoolmates without Klebold for support?

I think that Eric Harris would have done something terrible, whether it would be his schoolmates or not is an open question. What's really an open question with Eric is what the time frame would have been before he attacked.

And the older he got and the longer we waited for something to happen from him the worse it would have been. With each year he grew older, he got smarter and he had more resources. If it had been even a year later and he was moved out of the house, it would have been much worse. His parents were a limiting factor; he had to be careful about hiding stuff. Living on his own, he would have had a lot more freedom and a lot more money with a full-time job and a place of his own. He could have been buying truck loads of fertilizer like Tim McVeigh.

About 12 months before the attack, Jefferson County Sheriff's Department investigator Mike Guerra looked into threats by Eric Harris against a fellow student and drafted an affidavit seeking a warrant to search the Harris house based on information on Eric's Website about bombs. Why didn't he follow through and get a search warrant?

We don't know for sure. Guerra hasn't spoken to the press. But we have statements from Jefferson County that say Guerra was pulled away to another case, a multiple murder case. Then for whatever reason didn't come back to it.

What I tried to do in this book was look at the events from the point of view of the people in that story line and how they were looking at the world at that point. I asked myself: What made sense to them at that time, not what makes sense from our judgment looking back on these events.

It's very easy to point fingers. But when I look at the work that was done by the cops ahead of time, for the most part, I think it's very reasonable that they didn't see any threat coming with the information that they had at the time I don't think anyone would have.

This is the one particular moment where they should have. Guerra really put it together; Guerra really figured it out. I give him a lot of credit for having figured it out. But he got pulled away to another case, an actual murder, that's understandable.

Some of the cops I've spoken to about this have said: "You know how many complaints we get about some neighborhood brat who is causing mischief and making wild threats? It just becomes noise and static, and it's easy to dismiss." I think one of the lessons here and one that good cops have picked up on is: Don't be too quick to brush those things off because sometimes they are real.

What role did bullying play in this massacre?

Bullying did not play a role with Eric, who was the driver. There were at least a couple of cases of ongoing bullying that were documented at Columbine. What I didn't see was an excessive amount of bullying at Columbine.

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Psychologist and military historian Lt. Col. Dave Grossman, the author of "On Killing," has called first-person shooter video games "murder simulators." Do you think the killers' love of "Doom" played a role in conditioning them to kill?

I don't know if I'm qualified to answer that. I'm a little skeptical of any of the outside factors such as violent movies and video games and bullying because I don't see the killers telling me that.

That said, when it comes to video games, I have recently been told that I need to go back and do more research on this because there has been some research that does show some correlation between these types of video games and violent kids.

I'm always a little skeptical of that kind of research because causality is hard to prove. Just because you see a link statistically between a higher percentage of people liking violent video games is that cause or effect? Maybe violent kids like these violent games because they embody their fantasies.

A lot of blame for Columbine gets cast on "lax" gun laws, but the same gun laws-or even more relaxed gun laws-were in place in the sixties, seventies, and eighties. It's not just about access to guns. I knew gun enthusiasts in high school, and they weren't dangerous.

Right, and I think it's pretty clear that most of the people interested in guns aren't interested in mass murder. And so the access to guns is definitely not the driving force here.

I leave the gun issue up to the reader, but I think it's pretty clear if there were a way to keep guns away from kids, the killers would not have been able to do it. I don't know whether that's realistic or not.

One of the things that happened about this time in history was the birth of the World Wide Web. These kids came in as freshmen with the Web and that's an amazing amount of information that you get for free on anything, including bomb making.

Exactly. It's free and there's no audit trail, and no one is tracking it. It makes it much easier to get the "Anarchist's Cookbook" and you don't have to face questions from a librarian or bookseller.

Whether or not that really would have stopped anything is unlikely. A librarian or bookseller probably would not have turned [Harris in for getting bombmaking books]. But to a kid's point of view that sounds like a big obstacle. "How am I going to get the book without asking someone and tipping them off?" And I think those kind of things are natural inhibitors because the kid is perhaps more worried about that than he or she needs to be. But with the Web, they can go find anything and it's all private and anonymous. They can easily look over these things without anybody looking over their shoulders.

Could anything have been done to treat these kids and prevent this tragedy by helping them?

I don't think there was any way to help Eric. I think there were an extraordinary number of different ways to have helped Dylan. I'm not blaming anybody for not figuring this out with Dylan, but had he gotten treatment, he may well have not become a mass murderer.

Your book is really sympathetic to the frontline law enforcement officers at Columbine. Can you describe what they went through that day?

It was a metrowide call for assistance. And so you had all sorts of people responding, but they really didn't know what was happening. Quite a few people thought it was a terrorist attack because there were reports of bombs and automatic weapons.

There also seemed to be many shooters. They had so many different reports-and credible reports-of multiple shooters because Eric and Dylan took off their coats after they were first sighted.

Also the cops could tell there was heavy weaponry involved because the killers kept exploding pipe bombs in there and the walls of the building were shaking. So they knew something horrible was going on in there, but nobody knew what.

A lot of the cops were really frustrated. They were ordered to set up a perimeter. You know they were thinking: There's something terrible happening in there. Shouldn't I be doing something?

But I've been in the army and I think that sort of helps my perspective. I was in the infantry, and the last thing you want to do in a chaotic situation is add to the chaos and be the stupid lone wolf who goes off and complicates things further by charging in there by himself. You have to rely on your command and obey orders and do what you're told.

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Some of the accounts have attacked the officers. Some have even called them "cowards."

That's one of the things that frustrates me with some members of the public and the media about this: They fail to-or refuse to-put themselves into the shoes of the other person. It's sort of the wishful thinking way of looking at this [event].

They believe that the cops in that situation should have known what we know now and charged in there.

That's just silly. You have to put yourself in the shoes of a cop or commander arriving at that time and think what you're supposed to do. They did what the book said.

And they were operating under the intelligence they had at the time of the incident.

Absolutely. And here's an example of that: They thought the bombs had motion triggers. I don't know why JeffCo (Jefferson County Sheriff's Department) has never publicized this.

The diversionary bomb was set in the park, the killers drove away, and then, coincidentally, there was a surveying team out there. So a surveyor had his sextant out and the bag was in his line of sight. He went over there and moved the bag. Shortly thereafter, it erupted.

Anyway, he assumed that it went off because he moved it and that there was some kind of sophisticated motion detection device or something in there. There was nothing anywhere near that sophisticated in that bag. But he didn't know that. So he made a reasonable assumption. And so did the cops.

Could the police arriving at Columbine actually have saved the lives of any of the students?

Two officers arrived soon enough. But they are the only ones who are really relevant. The rest of the debate about whether the SWAT teams should have gone in sooner, it's all moot. The killing all took place in the first 15 or so minutes.

So the whole debate about whether the SWAT team should have gone in is largely moot, with the exception of Dave Sanders, obviously. And so the whole idea that most people have about the SWAT team should have charged the building, well that's sort of big picture thinking. But look at the details from the shooting, by the time SWAT was there, the killing had stopped.

Do you think the SWAT team could have gotten to Sanders faster? I mean the school was a 250,000-square-foot building that they had to clear.

I do think they could have gotten to Dave Sanders sooner. I don't understand why they didn't. That seems to me a failure of command. Outside the school they were getting reports of one guy bleeding to death; the students were holding a sign up in the window. Why they didn't react to that by breaking off a certain party or sending somebody else in there, I still don't understand.

The crime scene investigation of that school must have taken months.

Just the bullet and shell fragment log was like 30 pages of 25 to 30 lines per page. There's a thousand bullets and shell fragments. Each one is numbered in a little plastic baggy.

Mostly they had the FBI leading that. When the feds asked JeffCo if they needed help, JeffCo asked for FBI evidence teams.

Your book does an excellent job of dispelling some of the myths about Columbine: the Trench Coat Mafia, the bullying, Cassie Bernall's martyrdom, the assault on jocks. Why do you think we have so many enduring myths about Columbine?

We (journalists) started covering this story before we had any reliable data. So there was a lack of evidence and a lack of people who could evaluate the evidence we had [while journalists were working on deadline]. And you put those things together, and you've really got a mess. You've got bad analysis, and you've got bad data.

For example, the jocks. Eric had a complete list of people he didn't like. Jocks and preps were just some of them.

Eric disliked just about everybody. And he made comments in the library about a fat kid; he made fun of one kid for having big ostentatious glasses. He made fun of basically anyone he walked up to in that library and Dylan joined in. They walked up to a kid who was black, and they called him racial slurs.

He was tormenting his prey.

Exactly. Anything he could find to make fun of them. Yeah, he wanted to torment them.

In a recent Slate article, you talked about recent school shootings. Have we seen the same kind of planning and tactics as Columbine?

There have been quite a few that I would call just as diabolical and just as grandiose, just as horrifying, as Columbine was intended to be.

I've read studies that say that 1-2 percent of the American population has psychopathic tendencies. That means tens of thousands of kids going through high school. So why haven't we seen more Harrises?

A tiny, tiny percent of psychopaths are violent. They know that violence and murder brings the cops. And their whole lives are geared toward getting away with what the things they do. They like to win.

There is a convention in American journalism not to print the names of most rape victims. Maybe we shouldn't be printing the names of school shooters.

I think that is the one sort of reasonable solution I've heard. I'm not 100 percent sure it would work, but I think that's one I would be willing to get behind trying personally. Readers and viewers demand that we cover these event so we're going to do it. But leave a name out, we could do that.

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Eric says in his journal, I want to give people flashbacks. I'm going to terrorize you. You're going to remember me. What if we left the name of school shooters out of the papers? Would Eric have done this if he'd known his name wouldn't have been publicized?

I think part of him would be like: "I don't care if you squelched my name, I still screwed you people, and I still made you suffer every bit as much." I think a part of him would have said that. I don't know if the stronger part of him would be like: "Dammit, I want my name in the credits."

With somebody like Dylan-and I think Dylan is much more common, the angry and depressive guy who wants to lash out...He was like a suicide who also took people with him; he was a vengeful suicide.

What are some of the most effective measures that we now have in place to prevent another Columbine?

More than 80 percent of school shooters tell someone that they're going to do it, which is an astounding figure. If we listen to those people who tell us they're going to do it and act on that, we've wiped out 80 percent of the problem.

Another thing we've learned is that we need to communicate much better. Of course that's very easy conceptually, but it's hard to do, especially if we discourage kids from telling on their friends with "zero tolerance" policies.

Look at Columbine as a case study. If certain people had known everything about Eric, if any one person had known all of that, he or she would have stopped Columbine immediately.

Several groups have to communicate more. Cops and school officials, certainly, but in many cases mental health  professionals have to be in there, too. I think you saw that with Seung-Hui Cho at Virginia Tech.

And right now, a lot of schools won't pass on detailed information on kids to other schools in the chain. Don't get me wrong, a kid should be able to leave some of his past behind him. But we can allow elementary schools or high schools who believe they have a high-risk student to forward that information on to the next school in the chain. Schools should also be able to request backwards into the chain and ask for records on a particular student who may be dangerous.

It's easy with 20-20 hindsight to see that Eric Harris was a murderer waiting to happen, but can we really expect our educators and law enforcement officers to see these things coming?

We can expect them to see some of them coming. I think Eric Harris would be a particularly tough one to find. If there are future Erics out there they probably learned from Columbine, too. Luckily this kind of psychopath is fairly rare and most future threats are not going to come from psychopaths. And that's good because psychopaths have been eluding us forever.

Dylan and Eric talked a lot about wanting their lives to be a movie. Has your book been optioned? And if so, do you fear copycats?

No it hasn't been optioned, and I am hoping it will be. Still, I do worry about copycats. With the book I thought about it a long time, but I felt that worrying about making Columbine famous was kind of silly.

But a movie is a different kind of dilemma. Still, I don't think that Eric and Dylan come off very heroically in this story, especially in the end. It doesn't end well for them. Eric's statement "I want to leave a lasting impression on the world." I had that as the working title of the book for awhile. I interpreted it ironically. I can argue both ways whether Eric left a lasting impression. He left a profound impression, but how long lasting it will be I'm not sure. I don't think 100 years from now most people will know the name Columbine.

That means Eric won't have gotten this wish. I think he died knowing that he did not accomplish what he wanted to and most of his plan was a huge failure. The school was not burning down. He was not happy with the way this ended.

Editorial assistant Thi Dao helped with the production of this article.