Perhaps the most memorable case study was the Columbine High School shooting in Colorado in 1999, during which experts speculated about the influence of the game "Doom" on the teenagers who carried out that crime.

CNN: John D. Sutter,

Under Funes' conservative predecessor, teenagers could be arrested just for sporting gang tattoos without having committed any crime, filling the jails to dangerous levels.

MSN: El Salvador's gang truce cuts murder rate

The crime rate was higher in the 1960s and 1970s when many in that large generation were teenagers, an age when higher proportions of people commit crimes.

NPR: Reports Show Gun Homicides Down Since 1990s

The statistics may show a drop in crime across the country in the past five years, including a drop in murders by gun-wielding teenagers, but the fact is that each year more than 2, 000 Americans aged 14-17 use a gun to kill someone.

ECONOMIST: The lesson nobody learns