The young man arrested for the shooting in Michigan recorded a video where he expresses his intention to kill his companions

By Charlie Gile and Tim Stelloh -

ROCHESTER HILLS, Mich. - Authorities investigating a shooting that left four high school students dead in Michigan found video on the suspect's phone showing him talking about killing his classmates, a sheriff's official said Wednesday.

The disclosure was made prior to the appearance of the suspect, 15-year-old Ethan Crumbley, who was charged in Oakland County district court with four counts of first-degree murder, one count of terrorism and other crimes.

[The 15-year-old arrested for the Michigan shooting will be tried as an adult for terrorism: "It was not an impulsive act"]

Oakland County Sheriff's Lt. Tim Willis said the videos were recorded the night before Tuesday's shooting at the Oxford High School, an hour north of Detroit.

Students Who Survived Michigan Shooting Say Shooter Posed As Police

Dec. 1, 202103: 15

Authorities found a diary with annotations mentioning the shooting and the deaths of students.

Our sister network NBC News has not reviewed the videos or newspapers, and no additional information was immediately available.

The suspect's attorney, Scott Kozak, declined to comment.

Crumbley, who is on trial as an adult, has pleaded not guilty.

When asked by Judge Nancy Carniak if she understood her rights and the charges, she said, "Yes."

[The student who killed three of his classmates at a Michigan school shot more than 15 times]

Oakland County Prosecutor Karen McDonald said the shooting "was not just an impulsive act."

He said investigators had uncovered a "mountain" of evidence showing the attack was premeditated.

Two women hug in front of a small makeshift altar next to High School in Oxford, Michigan, honoring the victims of the shooting on December 1, 2021.Scott Olson / Getty Images

Another prosecutor, Marc Keast, said at the arraignment: "I honestly have no words to describe how horrible it was."

Recalling a security video of the shooting, Keast said the shooter entered a bathroom with a backpack and came out a few minutes later with a handgun.

In addition to the four people who died, seven others, including a teacher, were seriously injured.

Authorities said the shooter opened fire with a 9mm Sig Sauer pistol that the suspect's father had recently purchased.

[Carrying small arms in public without the need for a license is already legal in Texas]

The suspect was denied bail and will be booked into the Oakland County Jail, where he will be isolated from other inmates.

A probable cause hearing is scheduled for December 13.