The suspect behind the gun horror at Oxford High School in Michigan this week already contemplated killing other students before he followed through with the attempt, according to authorities.

Ethan Crumbley was the 15-year-old sophomore who opened fire at his high school and killed three students, and injured seven others on Tuesday, Nov. 30.

A fourth student was confirmed dead the following day.

Officials at the Oakland County sheriff’s office on Wednesday said the teen shooter filmed himself speaking about his bloody intentions the night before the tragic event, the New York Post reported. Similar notes were also found written in the journal found in his backpack.

According to the Associated Press, officials believed Crumbley also practiced using the weapon as he “posted pictures of the target and the weapon”.

They found a deleted Instagram account by the name of the suspect that read “now I am become Death, the destroyer of worlds. See you tomorrow, Oxford.”

Exactly what prompted the teen to think of causing bloodshed at school has not been identified since he invoked his rights to remain silent. While several of his classmates said he had been bullied, as Detroit Free Press reported, officials said he had no disciplinary history at school.

Nonetheless, the authorities cannot tolerate the reckless killing. Michigan prosecutors on Wednesday charged Crumbley as an adult with 24 counts following the violent gun attack, including murder and terrorism.

“He deliberately brought the handgun that day with the intent to murder as many students as he could,” said assistant prosecutor Marc Keast said during Crumbley’s arraignment.

If convicted, Crumbley would have to spend the rest of his life in prison. The teenage shooter pleaded not guilty.

Crumbley used a gun bought by his father just four days prior to the shooting. It had not been clear why the father bought it and how the teenager ended up possessing the firearm.

Prosecutor Karen McDonald said the parents of the suspect could also be charged.

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