A Michigan judge ordered accused school shooter Ethan Crumbley to stay locked up in a county jail as it was revealed he considered using Molotov cocktails during the November massacre that left four students dead.

Oakland County Circuit Judge Kwame Rowe said Tuesday that journal entries and text messages by Crumbley indicated the 15-year-old had previously made improvised incendiary weapons and weighed using the “Molotov cocktails” in the Nov. 30 school shooting, the Detroit Free Press reported.

Crumbley also admitted in his journal to starting a small fire in the woods and killing eight baby birds by “slowly torturing them,” Rowe noted in his 12-page opinion while denying the teen a transfer to a juvenile detention center from the Oakland County Jail, where he’s being held without bond.

The “prior delinquent acts are of grave concerns to this court,” Rowe wrote, adding that Crumbley could not be safely detained at the juvenile detention center in Pontiac.

“[Prosecutors] alleged that defendant planned and executed a mass murder at Oxford High School,” Rowe’s opinion continued. “Allegedly, he killed four student and injured seven others. The alleged facts speak for themselves.”

Prosecutors revealed last month Crumbley had texted his mother about “demons” and “ghosts” prior to allegedly gunning down his classmates and made Molotov cocktails at home.

The teen will be tried as an adult on charges of first-degree murder, assault with intent to murder, terrorism and gun counts in the school massacre. He pleaded not guilty in January and intends to pursue an insanity defense, his attorneys have said.

Prosecutors allege Crumbley’s parents, James and Jennifer Crumbley, gave the troubled teen the gun used in the attack as an early Christmas present. Attorneys for the Crumbleys claim they had no idea their son was planning on shooting up his school.

The couple, who have been charged with four counts of involuntary manslaughter, were ordered by a judge last week to stand trial — making them the first parents in the US to go on trial for their alleged roles in a mass school shooting, the Free Press noted. They’re being held on $500,000 bond at the same facility as their son.

Attorneys for Ethan, meanwhile, had argued that a county jail was not the proper facility for the teen, who is being kept away from adult inmates.

But Rowe noted that Ethan has managed to communicate with the public “several times a day,” including with emails he’s received from across the globe.

“I got a cell to myself, 3 meals a day, a TV to watch and the guards are pretty nice,” Ethan wrote in one Jan. 16 email, the Free Press reported.

In other writings, Ethan told a supporter their message had brightened his day and that photos of New York sent to him were “what he imagined,” according to the report.

“There is nothing in the email exchanges that cause this court concern regarding [Ethan’s] current mental health,” Rowe wrote. “He is eating, reading books, playing video games and talking to others.”

Attorney Paulette Loftin, who is representing the teen, was not available for comment, the Free Press reported. Ethan faces up to life in prison if convicted.

A review hearing for Ethan is set for March 24, the Detroit News reported.