New Delhi, April 22 -- The gunman who opened fire on tourists at Mexico's iconic Teotihuacan pyramids carried materials that were apparently related to the 1999 shooting at Columbine High School, authorities said Tuesday, a day after the attack that killed a Canadian woman and left at least 13 people injured.

Although officials did not mention Columbine by name, they referred to several books and handwritten notes that belonged to the gunman and referenced attacks in the United States in April 1999. Monday was the 27th anniversary of the massacre in Colorado.

Among the gunman's belongings was a photo modified by artificial intelligence showing him alongside the Columbine attackers, according to a state official who spoke to The Associat...