Today is the 15th anniversary of the Columbine High School massacre that left 13 victims dead and 27 others wounded. At the time, it was the worst school shooting in US history, although it was would have been much worse if the bombs planted by the killers, Eric Harris and Dylan Klebold, had gone off.

Dave Cullen was one of the first reporters on the scene, and spent the next decade digging into the story to uncover what really happened and why the two teenage boys did it. When his book, simply entitled “Columbine,” was published in 2009, I had an extended conversation with him, in which he revealed a lot of new information, and debunked a lot of what the media (and the sheriff’s department got wrong).

That interview is one of the most-downloaded podcasts on this site. You can listen to it here.