An 11-year-old boy opened fire in a private Mexican school on Friday, killing his 60-year old teacher and injuring five others. The sixth grader killed himself after.

Jose Angel Ramos, identified as a good student living with his grandmother, surprised his classmates and teacher when he entered their room with firing weapons in the morning of Friday. According to the police, he asked to go to the bathroom at the start of the school day but did not return. As his teacher went to look for him 15 minutes later, Ramos emerged with firing weapons and started shooting at his teacher and classmates.

According to Coahuila Gov. Miguel Angel Riquelme, Ramos was generally well behaved but voiced a strange warning before his rampage. “He was well behaved, but he told some of his classmates that ‘Today was the day,” he said.

While the police said that Ramos’ motive for the killing was not immediately clear, it was reportedly strange that the boy was dressed in the same clothes as Eric Harris, one of the killers in the Columbine 1999 massacre, when the incident happened. He was wearing black jeans, suspenders, and a white t-shirt bearing “Natural Selection” on the chest—the same shirt Harris wore when he and Dylan Klebold massacred 12 students and one teacher on April 20, 1999. This has led to speculations that he was under the influence of the violent first-person shooter video game linked to the Columbine massacre when he opened fire.

The police found that Ramos had been living with his grandparents since his mother passed away a couple of years ago. Despite that, Torreon mayor Jorge Zermeno described him as a good student, saying that there were no previous warning signs of him carrying out a tragic shooting. “Although he must have had some sort of a problem, the school say he was a normal boy with good marks and no outward signs of any behavioral issues,” said Zermeno.

Meanwhile, the five injured victims were all listed in stable condition as of Friday morning. Shortly after the incident, Mexican president Andres Manuel Lopez Obrador expressed his condolences to the relatives of the victims.