Investigators: Aztec High School shooter had timeline, deadly plans

• William Atchison entered the school Thursday morning by posing as a student.
• Atchison carried a backpack with a Glock pistol inside of it.
• Atchison had plans to hold a class hostage before killing the students and himself.

AZTEC — When students arrived at Aztec High School Thursday morning, former student William Atchison, 21, entered the school with them disguised as a student.

Police say Atchison carried a backpack with a Glock pistol inside of it. He also had a thumb drive with information on it about his plans to hold a class hostage, kill students and ultimately kill himself.

"He lived in Aztec with his parents, he worked at a local gas station and he planned this thing," said San Juan County Sheriff Ken Christesen.

Atchison shot and killed junior Francisco "Paco" Fernandez and senior Casey Marquez before taking his own life on Thursday.

"This person is not only a coward," Christesen said. "He's evil."

MORE:2 students killed, shooter dead after Aztec High School shooting

On a note he wrote at 6:51 a.m. Thursday, the shooter stated, "If things go according to plan today, today will be the day that I die."

He then described his plans to "gear up," hold a classroom hostage and "go apes--t" and then to "blow my brains out."

"Work sucks, school sucks, life sucks," the shooter wrote before the event. 

The note was found on the thumb drive he carried.

After he entered the school, Atchison went to the bathroom on the second floor, where he began getting ready for the shooting.

Fernandez had asked to be excused from class to go to the bathroom. He walked in on Atchison. State Police Chief Pete Kassetas said Fernandez had no chance to survive.

After he shot Fernandez, Atchison killed Marquez when he saw her in the hallway.

The school officials had heard the gunshots, and the school went into lockdown.

Custodian Thomas Hall pursued the shooter down the hallways, yelling for teachers to lock their doors.

Substitute teacher Kathleen Potter did not have the keys to lock the computer lab door.

She took the students into a supplies room and barricaded the door with a couch.

MORE:Suspect identified in Aztec High School shooting

Atchison entered the computer lab. Police say he knew where the students were in the supplies room, and he fired rounds toward them. None of the students were injured.

Christesen said Atchison didn't have a criminal history and was not on the Sheriff's Office's radar.

The only interaction Atchison had with police was during an FBI investigation last year.

Someone reported a message he wrote on an online gaming site asking about cheap assault rifles for a mass shooting. The FBI did not find any evidence of a crime being committed and ended the investigation. Police say Atchison claimed he had made the post as an Internet troll.

He did not have any weapons in 2016 and purchased a Glock legally last month in the San Juan County area, which he used in the shooting, according to police. 

When searching Atchison's house after Thursday's shooting, police found a note that outlined his schedule for the day. At 8 a.m., Atchison had planned to die.
Police say neither victim was targeted.

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Hannah Grover covers government for The Daily Times. She can be reached at 505-564-4652 or via email at hgrover@daily-times.com.