PONTIAC, Mich. >> The parents of four students killed at a Michigan school called on Monday for a state investigation of all aspects of the 2021 mass shooting, saying the convictions of a teenager and his parents are not enough to close the book.

The parents also want a change in Michigan law, which currently makes it hard to sue the Oxford school district for errors that contributed to the attack.

“We want this to be lessons learned for Michigan and across the country, ultimately,” said Steve St. Juliana, whose 14-year-old daughter, Hana, was killed by Ethan Crumbley at Oxford High School.

“But in order to get there, some fundamental things have to happen,” he said.

Buck Myre, the father of victim Tate Myre, said Michigan Attorney General Dana Nessel needs to “quit ignoring us.”

St. Juliana, Myre, Craig Shilling and Nicole Beausoleil sat for a joint interview with The Associated Press at the Oakland County prosecutor’s office. A jury last week convicted the shooter’s father, James Crumbley, of involuntary manslaughter.

The boy’s mother, Jennifer Crumbley, was convicted of the same charges in February. The parents were accused of making a gun accessible at home and ignoring their son’s mental distress, especially on the day of the shooting when they were summoned by the school to discuss a ghastly drawing on a math assignment.

The Crumbleys didn’t take the 15-year-old home, and school staff believed he wasn’t a threat to others. No one checked his backpack for a gun, however, and he later shot up the school.

The Oxford district hired an outside group to conduct an independent investigation. A report released last October said “missteps at each level” — school board, administrators, staff — contributed to the disaster. Dozens of school personnel declined to be interviewed or didn’t respond.

The district had a threat assessment policy but had failed to implement guidelines that fit the policy — a “significant failure,” according to the report.

Myre said a state investigation with teeth could help reveal the “whole story” of Nov. 30, 2021.

“When there’s accountability, then change happens,” he said. “We want accountability and change. No parent, no school district, no child should ever have to go through this.”

The state attorney general’s office disputes claims that it has no interest in Oxford. Spokesperson Danny Wimmer said Nessel has met with students and families but was rebuffed by the school board when she offered to investigate the shooting.

He said the state does not have authority to pursue its own civil investigation.

“We understand the families are hurting and are understandably upset, but this does not change the law,” Wimmer said.

An email seeking comment was sent to the school district. The criminal cases were handled by local prosecutor Karen McDonald.

Lawsuits by families against the district are pending in state and federal appeals courts, but the bar in Michigan is high. Under state law, public agencies can escape liability if their actions were not the proximate cause of injury, among other conditions.

And because of that legal threshold, the parents said, insurance companies that cover schools get in the way of public transparency.

“The system has been able to hold the people accountable,” Myre said, referring to the convictions of the Crumbley family, “but we are not allowed to hold the system accountable.”

“That’s unconstitutional,” he said. “That’s an attack on our civil rights.”

Myre praised Gov. Gretchen Whitmer for meeting with parents but said other officials have not listened.

St. Juliana said Michigan should create an agency dedicated to school safety, as Maryland has.

“We need to get the truth and the facts out there, and we can then develop the countermeasures to say, ‘How do we prevent these mistakes from happening again?’” St. Juliana said.

Besides Tate Myre and Hana St. Juliana, Justin Shilling, 17, and Madisyn Baldwin, 17, were killed. Six students and a staff member were wounded.

Ethan Crumbley, now 17, is serving a life prison sentence for murder and terrorism. His parents will be sentenced on April 9.