An 18-year-old student was arrested after a journal was found detailing plans to shoot his classmates at ACES High School in Everett.

According to the Everett Police Department, the 18-year-old’s grandmother called 911 Tuesday morning after finding the journal and believed the threats to shoot students at the school were credible.

Officers responded to the house on the 10600 block of Holly Drive and were shown excerpts of the journal and were told the grandson had a semiautomatic rifle stored in a guitar case. As officers reviewed the journal, they were alarmed by the statements and detailed plans to shoot students and use homemade explosives, according to a press release.

Excerpts from the journal show the teen had been thinking about the shooting frequently and wanted to make it "infamous," according to probable cause documents.

Court documents state the young man wrote, "I can't wait to walk into class and blow all those (expletives) away," and "I need to make this shooting/bombing infamous. I need to get the biggest fatality number I possible can."

Prosecutors allege the suspect had inert grenades in his bedroom that he planned to fill with black powder along with the AK-47 hidden in a guitar case.

The student attended Kamiak High School last year before transferring to ACES Alternative School this fall. Detective say he simply flipped a coin to determine which school to target. It came up ACES.

ACES High School was contacted and told about the threat. The student was arrested at the school, and a knife and marijuana were found on his person.

Mukilteo School District spokesman Andy Muntz said the teen was not on their radar, adding everyone is incredibly grateful for that grandmother's decision to turn the young man in.

"It really speaks to the importance of if you see something or hear something to notify the authorities. That's what she did. It could well have saved many, many lives including her grandson's life," said Muntz.

ACES student Olivia Fox said she was stunned at the accusations leveled against her close friend.

"There was lot of shock around the school when they released a picture of who it was," she said. "Me and a couple of his other good friends are shaken up, because we know how good of a kid he is."

KING 5 News is not releasing his name because he has not yet been formally charged.

The 18-year-old was booked at the Snohomish County Jail on probable cause for attempted murder due to planning and taking substantial steps toward executing a school shooting. The student is also facing an assault charge for allegedly kicking an officer after he slipped out of one of his handcuffs and tried to escape Tuesday.

The suspect made his first appearance in court Wednesday and is being held on $5 million bail.

His defense attorney said he has no prior criminal history whatsoever. However, police believe the teen used the same AK-47 to rob a convenience store on February 12. Court documents state he wrote in his journal about how powerful he felt because of how scared the female clerk was.