Mass murderer. Born on September 11, 1981, in Lakewood, Colorado. Dylan Klebold and his friend Eric Harris launched a deadly assault on their Colorado high school on April 20, 1999, during which they killed 13 people and injured more than 20. With a geophysicist for a father and a mother who worked with the disabled, he seemed an unlikely killer. He never wanted for anything. His family was upper middle class; his father had a successful mortgage business.

Intelligent, Klebold was in a program for gifted students at his elementary school. He was described as a shy child who loved baseball, especially the Boston Red Sox. By ninth grade, he was friends with Eric Harris and Brooks Brown. Like many teenagers, he liked violent video games. Klebold also enjoyed bowling and worked behind the scenes for school productions as a sound man. With Harris, he worked at a local pizza place for a time.

As a quiet teen interested in technology, Klebold didn't fit in with the dominant jock culture of Columbine High School. He developed a hatred of school – a sentiment shared by Harris. The two adopted the style of the school's outcast clique, the Trench Coat Mafia, wearing long coats, dark clothing, and looking unkempt, and reportedly hung around the group's periphery. Although he was bright, Klebold didn't apply himself in school and earned mediocre grades.

Klebold and Harris became interested in all things German, wore swastikas, and even gave the "Heil, Hitler" salute while bowling or playing card games. They also liked to play violent first-person shooter video games and listening to such German bands as KMFDM and Rammstein. The two started getting into trouble. In 1998, during their junior year, the two were arrested after they broke into a van and stole some things out of the vehicle. They were both charged with theft, criminal mischief, and criminal trespassing.

Since it was their first offense, they were enrolled in a diversion program, which consisted of community service and counseling. They were released a month early from program in February 1999. Both received glowing reports at the end of the program with Klebold being called "a bright young man who has a great deal of potential," according to an article in The Christian Science Monitor. Clearly, Klebold had successfully masked what was really going on with him.

Klebold, in personal writings found after the attack, expressed suicidal thoughts and was deeply saddened by his lack of a romantic relationship. There was also a lot of rage simmering under the surface as well, which appeared in the violent essays he wrote for English class and the stories and poems he wrote for his creative writing class – all of which often featured blood, death, and war. Another ominous sign of things to come, Klebold and Harris made a video of them acting as vigilantes shooting "jocks" in the school hallways for a school project.

Beginning some time in 1998, Klebold and Harris began to plan their attack on Columbine High School. They made acquired guns and made pipe bombs. A female friend of Dylan's reportedly helped them get three of the weapons – the same young woman he took to the prom shortly before the killings. The fourth weapon came from a co-worker at the pizza place. Harris even posted some of their bomb-making expertise and exploits on his website under his nickname "Reb" and using Klebold's nickname "Vodka."