Oakland County, Michigan, Prosecutor Karen McDonald outlined some of the key events that took place on the day of the shooting.
A teacher of shooting suspect, Ethan Crumbley, found a note on his desk on the morning of the shooting that "alarmed her to the point she took a picture of it on her cell phone."
She said the note included a drawing of a semiautomatic handgun pointing at the words, "the thoughts won't stop, help me." The note also included a section with a drawing of a bullet with the words "blood everywhere."
The parents of the suspect "were immediately summoned" to the school, McDonald said. The prosecutor noted that the suspect altered the note before it was retrieved by a counselor.
"At the meeting James and Jennifer Crumbley were shown the drawing and were advised that they were required to get the — their son into counseling within 48 hours," she said.
The prosecutor said the parents "failed to ask their son if he had his gun with him or where his gun was located and failed to inspect his backpack for the presence of the gun which he had with him."
The parents resisted the idea of their son leaving the school at that time and they left the school without him, she added. He was returned to the classroom.