OXFORD TOWNSHIP, Mich. (NewsNation Now) — Michigan Attorney General Dana Nessel said her office won’t be the agency to conduct a school district’s third-party investigation into the events at Oxford High School that occurred before last week’s school shooting that left four students dead.

Oxford Community Schools Superintendent Tim Throne has said a third party will investigate. Nessel had offered that her office could conduct it, but she said in a statement Monday evening that the school district had declined her offer.

“Despite this outcome, my department will continue to support the ongoing criminal investigation in Oakland County and looks forward to meeting with parents, students and teachers when they are ready to share their thoughts,” she said. Nessel has said she could still investigate.

Oakland County Prosecutor Karen McDonald, who is overseeing the criminal case against the student accused in the Nov. 30 shooting and who took the rare step of charging his parents, left open the possibility Monday that school officials could also face charges, saying, “In this case, a lot could have been done different.”

She noted that three hours before Ethan Crumbley allegedly opened fire, killing four peers and wounding six others and a teacher, the 15-year-old was sent back to class after a meeting between school counselors and his parents over a drawing a teacher found on his desk that included a bullet and the words “blood everywhere.”

Throne said Crumbley and his parents met with counselors on the day of the shooting. He said counselors found the teen “calm” and didn’t believe he would harm others. The parents, Jennifer and James Crumbley, were asked to take their son home but “flatly refused,” Throne said.

Crumbley has been charged as an adult with murder, terrorism and other crimes in the attack. And McDonald filed involuntary manslaughter charges against his parents, saying they failed to intervene on the day of the tragedy despite being confronted with the drawing and its disturbing message.

Authorities say Ethan used a 9mm semi-automatic pistol to carry out the attack, and that his father bought it for him at a local gun shop on Black Friday as an early Christmas present. Although the gun was legally sold to James Crumbley, minors in Michigan cannot possess guns aside from limited situations, such as when hunting with an adult.

The Crumbley parents were taken into custody on Dec. 4 after they were caught hiding inside in the Detroit studio of artist Andrzej Sikora. The artist’s attorney said Sunday that he is cooperating with investigators and didn’t know the couple was facing charges or that they had stayed overnight at his studio while authorities were searching for them.

The couple’s attorneys have said they didn’t intend to flee.