A sign encourages prayer outside an ice cream shop Friday, Dec. 8, 2017, in Aztec, N.M., following this week's shooting at a high school. A 21-year-old gunman who disguised himself as a student to get into a New Mexico high school where he killed two students had caught the attention of U.S. investigators more than a year ago, authorities said Friday. William Atchison, a former student at small-town Aztec High School, had legally purchased a handgun at a local store a month ago and planned the attack, authorities said. (AP Photo/Russell Contreras)

In this Thursday, Dec. 7, 2017 photo, hundreds of people raise their candles during a candlelight il at Minion Park in Aztec, N.M. A shooting at Aztec High senior, in the small New Mexico town, left two students and the suspect dead, authorities said Thursday. (Marla Brose/The Albuquerque Journal via AP)

In this Thursday, Dec. 7, 2017 photo, Bianca Martinez, center, an Aztec High senior, grieves with friends during a candlelight vigil at Minion Park in Aztec, N.M. A shooting at the high school in the small New Mexico town left two students and the suspect dead, authorities said Thursday. (Marla Brose/The Albuquerque Journal via AP)

Aztec High School students and area residents gather for a candlelight vigil in Aztec, N.M., Thursday, Dec. 7, 2017, after a shooting at the high school. Students hid in their classrooms, some behind locked doors, as a suspect opened fire Thursday inside the school, killing two classmates before he died. (AP Photo/Russell Contreras)

Aztec High School is shown in Aztec, N.M., Thursday, Dec. 7, 2017. Students hid in their classrooms, some behind locked doors or in closets, as a gunman opened fire Thursday inside a New Mexico high school, (AP Photo/Russell Contreras)

People gather for a vigil at St. Joseph Church in Aztec, N.M., Thursday, Dec. 7, 2017, Students hid in their classrooms, some behind locked doors or in closets, as a gunman opened fire Thursday inside a New Mexico high school, (AP Photo/Russell Contreras)

People gather for a vigil at St. Joseph Church in Aztec, N.M., Thursday, Dec. 7, 2017. Students hid in their classrooms, some behind locked doors or in closets, as a gunman opened fire Thursday inside a New Mexico high school. (AP Photo/Russell Contreras)

In this undated photo provided by the San Juan County Sheriff's Office, is a note investigators found in a trash can in William Atchison's room during a search after a shooting at Aztec High School in Aztec, N.M. on Thursday, Dec. 7, 2017. A 21-year-old gunman who disguised himself as a student to get into a New Mexico high school where he killed two students had caught the attention of U.S. investigators more than a year ago, authorities said Friday. At Atchison's home, investigators found a torn note in a trash can in his room that listed what they believed to be the timeline for Thursday's shooting. The last words written on the note read "die." (San Juan County Sheriff's Office via AP)

In this undated photo provided by the San Juan County Sheriff's Office is William Atchison. A 21-year-old gunman who disguised himself as a student to get into a New Mexico high school where he killed two students had caught the attention of U.S. investigators more than a year ago, authorities said Friday, Dec. 8, 2017. Atchison, a former student at small-town Aztec High School, had legally purchased a handgun at a local store a month ago and planned the attack, authorities said. (San Juan County Sheriff's Office via AP)

A San Juan County Sheriff's deputy prepares for a press conference in Aztec, N.M. on Thursday, Dec. 7, 2017, after a school shooting at the city's high school. Students hid in their classrooms, some behind locked doors, as a suspect opened fire Thursday inside Aztec High School, killing two classmates before ending up dead. (AP Photo/Russell Contreras)