The father of the teen who opened fire on a Michigan high school in 2021, killing four classmates, could have prevented the "nightmare," a prosecutor said during opening arguments Thursday in the trial of James Crumbley, who could potentially become the second parent of a school shooter to be convicted, following his wife. 

"This nightmare - these murders - were preventable by him, foreseeable by him," assistant prosecutor Marc Keast told the jury, the Associated Press reported.

Keast said that four days before Ethan Crumbley, 15, unleashed the carnage at Oxford High School, his father bought a Sig Sauer 9 mm handgun with his son.

The day of the shooting, the elder Crumbley did not inform school officials about the purchase, nor did he say he took his son to a pistol range the same weekend, when he and his wife were confronted by school officials about a disturbing drawing found on Ethan's math homework, the wire service said.

The drawing consisted of a gun similar to a Sig Sauer, along with drops of blood, a bullet, and the chilling phrase: "The thoughts won't stop me."

Ethan's mother and father did not take their son home - and the school, fearing he would commit suicide, didn't demand it. Ethan's backpack went unchecked.

The bloodbath took place later that afternoon.

"Instead of seizing that incredible opportunity, James Crumbley spent hours making deliveries" for DoorDash, Keast said, the AP reported.

Crumbley faces four counts of involuntary manslaughter, one for each of the students killed at the school in November 2021. Another seven students were wounded. 

The father isn't being tried on whether he knew what his son had planned, but is accused of being negligent for not properly securing the weapon. 

"This case isn't about bad parenting - it's not illegal to be a bad parent. It's not kids doing kid things," Keast said. "We're talking about preventable mass murder."

Crumbley's wife, Jennifer, was found guilty of four counts of involuntary manslaughter last month and could get up to 15 years in prison when she is sentenced in April.

The father's defense lawyer, Mariell Lehman, suggested that Crumbley will testify on his own behalf.

"James Crumbley was not aware that his son had access to that firearm," Lehman said. "You will hear testimony that access was not allowed in James Crumbley's mind. You will not hear that James Crumbley suspected that his son was a danger."

Ethan was sentenced to life in prison last September.