Watch: Prosecutor explains why teen shooter's parents are being charged

In a news conference today, prosecutor Karen McDonald announced that the parents of Ethan Crumbley — the teen accused of killing four people at a Michigan high school — have each been charged with four counts of involuntary manslaughter.

"I'm announcing charges against the shooter's parents, Jennifer and James Crumbley," she said at a news conference today (see first tweet below).

McDonald then outlines the disturbing event that happened at school hours before the shooting (second tweet below), when the boy and his parents were called into the school office about horrific images he had drawn, including a person who is shot, along with "a semi-automatic handgun pointing at the words 'The thoughts won't stop. Help me,'" and "a drawing of a bullet with the following words above that bullet: ' Blood everywhere.'"

Other messages in those drawings included, "My life is useless," and "The world is dead."

Although the boy was in the meeting where these gruesome messages were being discussed, and his parents knew there were guns in their house, nobody thought to check his backpack, which was right there in the room with them.

The parents also "resisted the idea of their son leaving the school at that time. Instead, James and Jennifer Crumbley left the school without their son." Why the school didn't force him to leave with his parents is unclear.

The thought that their son was capable of doing such a heinous act did cross the Crumbleys' minds, however. From CBS:

After news of the shooting broke, Jennifer sent a message to Ethan at 1:22 pm, reading: "Ethan. Don't do it." Almost 15 minutes later, James called 911 and reported a gun missing from his house, telling first responders he believed his son was the active shooter at the high school, according to McDonald.