This has been discussed at length on other FR threads.
The father bought the handgun on Black Friday with son present. On Saturday the mother posted a picture of the gun on social media captioned “Mom & son day testing out his new Xmas present”.
A few hours before the shooting, the parents were called to the school after
A drawing of a semi-automatic handgun pointing at the words, “The thoughts won’t stop. Help me.”
A drawing of a bullet with “blood everywhere” written above the bullet.
A drawing of a person who appeared to have been shot twice and bleeding.
A drawing of a laughing emoji.
Writing that said, “My life is useless.”
Writing that said, “The world is dead.”
At the meeting, the parents were asked to take the boy home and were given 48 hours to get him into counseling. The parents declined to take him home and left him at the school. During the meeting, the gun and ammo and notebook with his plans to shoot other students were right there in his backpack.
When the father heard about the shooting, suspecting it was his son, he rushed home to check on the gun and found it missing.
There’s more, but you can look it up for yourself. It sounds to me, based on reports, like the parents were um, not thinking straight (to put it mildly). Knowing he had access to a new handgun he considered his own, then seeing his disturbing drawing and words and cry for help at the school meeting, they really should have taken him home and confiscated the backpack.
I have not seen evidence they saw the drawing. At least one report said that by the time they saw the drawing, all the disturbing stuff had been drawn over to make it illegible.