By Andrew Hay

TAOS, New Mexico (Reuters) – A gunman who killed two students at a New Mexico high school and then took his own life was a former student who was investigated by the U.S. Federal Bureau of Investigation last year after he asked online about buying weapons for a mass shooting, officials said on Friday.

Authorities identified the shooter in Thursday’s attack as 21-year-old William Atchison, who worked at a gas station in Aztec, New Mexico, and was an enthusiast of active shooter gaming websites.

“He was a single coward shooter,” San Juan County Sheriff Ken Christesen said at a news conference by law enforcement. “It’s important to understand how focused he was, how deranged he was, in his intent.”

The shooting occurred shortly after 8 a.m. on Thursday at the high school in Aztec, a town of 6,000 people about 200 miles (320 km) northwest of Santa Fe and 20 miles (32 km) from the Navajo Nation reservation.

Atchison disguised himself as a student, entered the school as students got off buses, and was in a bathroom preparing for the shooting when Francisco Fernandez, a pupil at the school known for his computer skills, entered the restroom, officials said.

Atchison shot Fernandez, then exited the bathroom and shot cheerleader Casey Jordan-Marquez in the hallway, said New Mexico State Police Chief Pete Kassetas.

Atchison fired randomly in the hallway before entering a computer lab and firing through a wall at students barricaded inside a closet, Kassetas said. Atchison likely shot himself shortly afterwards as police entered the school, he added.

Police found a thumb drive on Atchison’s body that contained a Dec. 7 message indicating he was unhappy with work and life, and he planned to attack a school.

“If things go according to plan, today would be when I die,” the message read.

In March 2016, Atchison was interviewed by the FBI, which had acted on a tip about a comment he made on an online gaming site.

“If you’re going to conduct a mass shooting does anyone know about cheap assault rifles?” FBI special agent Terry Wade said Atchison asked.

The FBI closed its investigation after determining no crime was committed, Wade said.

Atchison did not have any weapons when the FBI interviewed him, officials said. He purchased the 9mm pistol he used in the shooting locally and legally last month, officials said.

(Reporting by Andrew Hay; Writing by Suzannah Gonzales; Editing by Colleen Jenkins and Diane Craft)