Authorities investigating a shooting that left four high school students dead in Michigan found videos on the suspect’s phone that showed him talking about killing students, a sheriff’s official said Wednesday.
The disclosure was made before the arraignment of the suspect, Ethan Crumbley, 15, who was charged in Oakland County district court with four counts of first-degree murder, one count of terrorism causing death and other crimes.
Oakland County Sheriff’s Lt. Tim Willis said the videos were recorded the night before the shooting Tuesday at Oxford High School, about an hour north of Detroit.
Authorities found a journal with entries that mentioned shooting and killing students.
NBC News has not reviewed the videos or the journals, and additional information about them was not immediately available.
The suspect’s lawyer, Scott Kozak, declined to comment.
Crumbley, who is being tried as an adult, pleaded not guilty. When Judge Nancy Carniak asked whether he understood his rights and the charges, he said, “Yes.”
Oakland County Prosecutor Karen McDonald said the shooting was “not just an impulsive act.” She said investigators had uncovered a “mountain” of evidence showing that the attack was premeditated.
Another prosecutor, Marc Keast, said at the arraignment, “I honestly don’t have the words to describe how horrific that was.”
Recalling a security video of the shooting, Keast said the shooter walked into a bathroom with a backpack and emerged a few minutes later with a gun.
In addition to the four people who died, seven others, including a teacher, were seriously wounded. Officials said the shooter opened fire with a 9 mm Sig Sauer handgun that the suspect’s father had recently bought.
The suspect was denied bond and will be transferred to the Oakland County Jail, where he will be isolated from other inmates.
A probable causing hearing is scheduled for Dec. 13.
This story first appeared on NBCNews.com.