The jury foreperson in the trial of Jennifer Crumbley said the guilty verdict wasn’t immediately unanimous, but evidence presented in trial including her son’s notebook writings played a “huge part.”

Crumbley was convicted of all four counts of involuntary manslaughter Tuesday, with the jury holding her criminally responsible for the shooting carried out by her son, Ethan Crumbley, at Oxford High School on Nov. 30, 2021.

It was an unprecedented, unanimous decision as it marked the first time in the United States that a parent has been held responsible for their child carrying out a mass school shooting.

“Speaking for myself, I know that each individual juror had their own opinion,” the jury foreperson, Alex, whose last name was not disclosed for her own privacy, told NBC’s “TODAY” show Wednesday. “For me, I just feel like Jennifer didn’t separate her son from the gun enough to save those lives that day.”

She noted how the mother was the last person known to have had custody of the gun before her son used it in the shooting.

“And I think the responsibility of securing the weapon then falls on her,” Alex said. 

Host Savannah Guthrie asked her: “What about those text messages or journal entries or things that jurors saw that indicated Ethan had asked for help and his parents hadn’t given him that help, was that persuasive to you?”

“To me personally, it wasn’t as impactful as the evidence of her having the gun, but I know for my fellow jurors, the notebook played a huge part,” Alex said.

Crumbley, 45, faces up to 15 years in prison per count. Sentencing is scheduled for April 9.

Her husband, James Crumbley, has also been charged with four counts of involuntary manslaughter. He has pleaded not guilty and is set for trial next month.

Ethan Crumbley, 15 years old at that time, opened fire at Oxford High School in Oxford, Michigan, with a 9 mm Sig Sauer handgun that his father had purchased and given him days before, prosecutors have said.

He killed Madisyn Baldwin, 17; Tate Myre, 16; Hana St. Juliana, 14; and Justin Shilling, 17, and wounded seven others.

Ethan Crumbley, now 17, is serving life in prison without the possibility of parole after pleading guilty in October 2022 to charges that include terrorism causing death and first-degree premeditated murder.

The cases against the Crumbleys are among the rare instances of parents being charged after their children conduct mass shootings.

At the trial, the prosecution portrayed Crumbley as a neglectful mother. When she and her husband gave their son the semi-automatic handgun, prosecutors said, neither properly stored it.

On the day of the shooting, after the Crumbleys had been summoned to the school because of a disturbing drawing of a gun made by their son, the parents didn’t tell school officials that he had access to a weapon or take him home.

Robert Crimo Jr., the father of a man accused of killing seven people in a mass shooting at a Highland Park, Illinois, Fourth of July parade was criminally charged, and he pleaded guilty to misdemeanor counts in November.

Crimo Jr. pleaded guilty to counts related to sponsoring his son’s Firearm Owners Identification application, which allowed Robert Crimo III to buy the AR-15-style weapon used in the shooting. 

Authorities said the father did so when Crimo III was too young to apply and despite previous threats by the 19-year-old to harm himself and loved ones.