Key moments surrounding Michigan high school shootings

A prosecutor has charged the parents of a 15-year-old boy who is accused of killing four students and wounding others in a shooting at a Michigan high school this week.

James and Jennifer Crumbley face involuntary manslaughter counts after Tuesday's mass shooting in Oxford Township, about 50km north of Detroit. Here is a timeline of events before the rampage and what has happened since:

Friday, November 26: James Crumbley buys a 9mm Sig Sauer from Acme Shooting Goods in Oxford, according to Oakland County Prosecutor Karen McDonald. His 15-year-old son Ethan later posts a photo on Instagram of himself holding the semi-automatic handgun, writing: "Just got my new beauty today. SIG SAUER 9mm. Any questions I will answer." He includes an emoji of a smiling face with heart eyes.

Jennifer Crumbley. Photo / AP

Saturday, November 27: Jennifer Crumbley, Ethan's mother, writes on social media that it is a "mom and son day testing out his new Christmas present", the prosecutor says.

Monday, November 29: A teacher sees Ethan, a sophomore at Oxford High, searching online for ammunition with his cellphone during class and reports it to school officials, McDonald says. School personnel call his mother, leave a voicemail and email her. She does not respond. While exchanging text messages with her son, she writes: "Lol. I'm not mad at you. You have to learn not to get caught."

That night, Ethan Crumbley records a video in which he discusses killing students, according to sheriff's Lt Tim Willis.

Oakland County prosecutor Karen McDonald. Photo / AP

Tuesday, November 30: A teacher finds a note on Ethan's desk that alarms her enough to take a photo, the prosecutor says. It includes a drawing of a handgun and the words: "The thoughts won't stop. Help me." Also depicted is a bullet with the words "blood everywhere" above a person who appears to have been shot twice and is bleeding. A laughing emoji is drawn below the figure. The note also says "my life is useless" and "the world is dead".

James and Jennifer Crumbley. Photo / AP

The parents are immediately summoned to the school for a meeting that occurred around 10am. A school counsellor removes Ethan from the classroom and takes him to the office with his backpack. The counsellor obtains the drawing, but Ethan has already scratched out portions. The parents are shown the note and advised that they are required to get him counselling within 48 hours. They resist the idea of Ethan immediately leaving school and depart without him, McDonald says. He returns to the classroom.

James Crumbley. Photo / AP

About 12.51pm, Ethan emerges from a bathroom with the gun his father bought four days before. He fires at students in the hallway, killing four and wounding six students and one teacher. Deputies capture him within minutes of the shooting. When news of an active shooter becomes public, Jennifer Crumbley texts her son at 1.22pm: "Ethan don't do it." Fifteen minutes later, at 1.37pm, James Crumbley calls 911 to report that a gun was missing from his house and he believes his son may be the shooter. The gun had been kept unlocked in a drawer in the parents' bedroom, McDonald says.

Wednesday, December 1: Ethan is charged as an adult with murder and terrorism.

Friday, December 3: James and Jennifer Crumbley are charged with involuntary manslaughter.