OXFORD TOWNSHIP, Mich. (NewsNation Now) — After four students were killed in a school shooting in Michigan last week, questions remain around why the student charged in the attack was allowed to go back to class after a disturbing note he had written was discovered.

Oxford Community Schools leaders have declined requests for interviews, despite calls from the community demanding answers. On Friday, the head of the district released a letter to parents detailing its version of events.

According to the letter, a teacher reported Ethan Crumbley’s drawing of a gun pointing to the words “The thoughts won’t stop. Help me,” to the school counselors and the dean of students Tuesday. Crumbley was brought to the guidance office.

His parents were called in, but the district says they refused to take him home and he was returned to class.

In the letter to parents, the superintendent defended school staff, saying the counselors made a decision based on their experience and did not have all the facts we know now.

Michigan Attorney General Dana Nessel told NewsNation on Sunday that “anything is possible” when it comes to potential criminal charges for the school officials who were made aware of the student’s alarming behavior.

“I don’t want to jump to any conclusions because again, we don’t have that information at this point,” Nessel said. “But that is a big part of the investigation. People want to make sure that these questions are answered.”

“I see a lot of negligence, but I don’t foresee charges against anyone in the school,” said David Steingold, a Detroit-area defense attorney. “You would have to show specific intent. No one on the staff intended to commit a crime.”

As for others, the gun was legally sold by a local dealer to James Crumbley, according to investigators. The gun manufacturing industry is protected from civil lawsuits for its products, according to the Giffords Law Center, which tracks gun issues.

Crumbley has been charged as an adult with murder and terrorism, along with other crimes. His parents were arrested early Saturday morning after a manhunt led police to a Detroit warehouse. The parents’ car was spotted outside.

“They are in our jail,” Sheriff Michael Bouchard said. “All three of them. The son and both parents segregated individually in isolation.”

The Associated Press contributed to this report.