MONTPELIER, Vt. — A Vermont teenager accused of planning “to shoot up” his former high school wrote in a diary he titled “Journal of an active shooter” that he had “big plans” to kill as many as he could.

Jack Sawyer, 18, had recently returned to Vermont from a Maine treatment center for troubled teens. In his journal acquired by the Rutland Herald, he listed the guns and ammunition needed and his recurring plot to shoot up Fair Haven Union High School.

The Poultney, Vermont teen also wrote of his mental health struggles, suicidal thoughts and appreciation and love for his family.

“I don’t care anymore who I kill, or when I kill, I just know that one day it’ll happen,” he wrote on Dec. 28.

On Friday, Sawyer pleaded not guilty to charges of attempted aggravated murder and other offenses. His arrest the day before, and the deadly Florida high school shooting, has invigorated gun control efforts in the Vermont state Legislature.

Police said they were tipped to Sawyer by a girl with whom he had attended the treatment facility. They were messaging online when Sawyer revealed his plans.

“It was only by the grace of God and the courage of a young woman who spoke up that we averted a horrific outcome,” Republican Gov. Phil Scott said.

Police said Sawyer had recently bought a shotgun and four boxes of ammunition. He also told police he had read books about school shootings.

On Nov. 29, he wrote in his journal: “I’ve realized the huge importance of being able to kill the kids that I actually know vs. waiting a year or so until they’re all gone.”

He wrote Jan. 23 that he was planning to sit in the parking lot and scope out the school to determine the school resource officer’s schedule.

“Then I will gear up and let loose my anger and hatred. It’ll be fantastic,” he wrote.

He also apologized to his family, who he said he loves, and that he appreciated all they had done for him, and the money spent on his treatment.

His family could not be reached for comment. A phone rang unanswered at his father’s home. Vermont Defender General Matthew Valerio, whose office is defending Sawyer, said there are a lot of unproved allegations.

“I have a sense that this case is a lot different than initially portrayed,” Valerio said.