Crime New Mexico High School Shooter ID'd as Former Student, 21: 'He Was Focused and He Was Deranged' "He was determined to create as much carnage as he could," San Juan County Sheriff Ken Christiansen said on Friday By Chris Harris Chris Harris Twitter Chris Harris has been a senior true crime reporter for PEOPLE since late 2015. An award-winning journalist who has worked for Rolling Stone and MTV News, Chris enjoys prog rock, cycling, Marvel movies, IPAs, and roller coasters. People Editorial Guidelines Published on December 8, 2017 02:52 PM Share Tweet Pin Email The 21-year-old gunman behind Thursday’s fatal high school shooting in New Mexico was known to the Federal Bureau of Investigation and infiltrated the school building that morning by disguising himself as a student, according to investigators. Once inside Aztec High School, William Atchison killed two students as part of a broader plan that was outlined for police in documents he had uploaded to a thumb drive recovered from his clothing. “He was focused and he was deranged,” San Juan County Sheriff Ken Christiansen told reporters at a news conference on Friday. That’s when authorities also confirmed the shooter’s identity and, for the first time, provided further details about how the attack was carried out. Detectives believe the gunman did not know his two victims, Francisco Fernandez and Casey Marquez, but said he had attended Aztec High School years ago. He did not graduate from school, having moved out of the district before his senior year. “If things go according to plan, today [will] be the day I die,” read one note found among Atchison’s files on his thumb drive, authorities said Friday. San Juan County Sheriff's Office The document went on to lay out the rest of his scheme: He would find a place inside Aztec High to “gear up” with his 9 mm handgun and multiple magazines and then find a classroom to hold hostage, “then go apes— and then blow my brains out.” The message also expressed the gunman’s hatred for the state of New Mexico, authorities said — but beyond that, they were not commenting on a possible motive, Sheriff Christiansen said Friday. He said the killer’s gun was purchased “locally and legally” and that he lived in Aztec with his parents, worked at a gas station, and had no record — not even a traffic ticket. “He’s not only a coward, he’s evil,” the sheriff said. • Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter. At the Friday news conference, investigators detailed a timeline of the shooting, saying Atchison walked into the school around 8 a.m., blending in with the throngs of students heading for class. He found a vacant second-floor bathroom to prepare, Christiansen said. With the halls largely emptied and the school day underway, the shooter headed for the bathroom door just as Fernandez was entering. Fernandez — reportedly a football player known to his family and friends as “Paco” — “had absolutely no chance to survive that encounter,” New Mexico State Police Chief Pete Kassetas told reporters. After shooting Fernandez, the gunman exited into the hallway where he encountered Marquez, a cheerleader. “He immediately shot her dead,” Kassetas said. Upon hearing the gunfire, staff at the school sprang into action, barricading doors and leading students to safety. Facebook “He walked up and down the hallway, firing randomly and shooting into classrooms,” Kassetas said. He also yelled, “I know you’re in there!” No one else was struck by a bullet, even though the shooter reloaded multiple times, according to Kassetas. Authorities arrived within a minute of being notified of the shooting. As they entered the school building, the shooter took his own life. • For more compelling true crime coverage, follow our Crime magazine on Flipboard. “He was determined to create as much carnage as he could,” Christiansen said, noting Fernandez’s presence likely saved other students by triggering the attack prematurely. During the news conference, Terry Wade, the FBI special agent in charge in Albuquerque, said the shooter had belonged to an online gaming forum and, in March 2016, posted a question about the best guns to use in mass shootings. He did not own a firearm at the time. After that, federal investigators interviewed him and his family and he told agents he had no plans for an attack. The FBI closed the investigation when it determined no crime was committed. Authorities said Friday their investigation remains ongoing and that they continue to pour over the recovered thumb drive and the shooter’s home computers for insight into what drove him to kill.