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The exact reasons a teenage gunman shot his fellow students and teachers last month at a Santa Fe (TX) High School remain a mystery. His model for carrying it out is more clear.

The 17-year-old junior wore a black trench coat and fired a sawed-off shotgun, the same attire and weaponry used by the two gunmen who killed a dozen students and a teacher at Columbine High School in Colorado in 1999, the New York Times reports.

He wore a T-shirt with the phrase “Born to Kill” on it in bold, similar in design to those worn by the Columbine attackers, which read “Wrath” and “Natural Selection.”

His crude arsenal included canisters of carbon-dioxide gas and Molotov cocktails, two types of explosives used by the Columbine gunmen.

The picture he had posted of his trench coat on Facebook showed a small red-star medallion with the Communist hammer-and-sickle on the collar, the same type of button a Columbine gunman attached to his boot.

It was not the first time a high school suddenly engulfed in gunfire and death found itself looking for clues in the random symbology of a nearly 20-year-old mass shooting that has become, it seems, the standard by which youthful gunmen across America have come to measure themselves.