Six Americans were among those injured on Monday when a gunman opened fire at Mexico's Teotihuacán pyramids, a popular tourist destination.The gunman, identified by Mexican authorities as Julio César Jasso Ramírez, allegedly visited the pyramids on several occasions to engage "in reconnaissance of the specific locations he intended to utilize for his violent attack," according to officials. One Canadian was killed and 13 others were injured.SIGN UP TO GET TRUE CRIME NEWSLETTERAmong the others injured are six people from the U.S., and other individuals from Russia, Brazil, the Netherlands and Canada, officials said.Law enforcement in the region received initial reports of the shooting at 11:20 a.m. local time on Monday. The National Guard quickly responded to the scene, with officials adding that the gunman took his own life at 11:45 a.m.SEND US A TIP HEREOne tour guide who was at the scene told The Associated Press that the gunman fired upward."Some people, because they were scared ... threw themselves face-down on the ground, and the rest of us started to go down," the tour guide said.LISTEN TO THE NEW 'CRIME & JUSTICE WITH DONNA ROTUNNO' PODCASTDuring a news conference on Tuesday, Mexican officials said they found "literature, images, and handwritten manuscripts, all allegedly related to violent events known to have occurred in the United States in April 1999" in the gunman's backpack, referring to the Columbine High School shooting. That shooting took place on April 20, 1999.Officials said the gunman was carrying 52 live rounds of .38 Special caliber ammunition inside a plastic bag, along with a knife.LIKE WHAT YOU'RE READING? FIND MORE ON THE TRUE CRIME HUBMexican President Claudia Sheinbaum addressed the shooting in a social media post on Monday."What happened today in Teotihuacán deeply pains us. I express my most sincere solidarity with the affected individuals and their families," she wrote. "Yesterday’s attack highlights the urgent need to strengthen our security protocols."José Luis Cervantes Martínez, the attorney general of the state of Mexico, said that investigators built a "psychopathic profile" of the gunman, which was "characterized by a tendency to copy situations that occurred in other places, at other times and involving other figures."The Teotihuacán archaeological site will be closed until further notice after the shooting, the National Institute of Anthropology and History said in an announcement.The Associated Press contributed to this report.