authorities detail what really is a chilling warning signs that occurred in the days leading up to this tragedy. cnn s tom foreman now takes an in-depth look at the timeline of events. reporter: before the gunfire the terrified students, police and ambulances there were warnings. there was absolute reason to believe this individual was dangerous and disturbed. reporter: authorities suggest the immediate trouble starts november 26th, when james crumbley takes his 15-year-old son ethan to buy a sig sauer 9-millimeter pistol at a local gun shop. although the dad fills out the paperwork, the son posts a picture on social media. along with the caption just got my new beauty today. no. no. legally that s not his. reporter: the sheriff says by law the gun can t actually belong to the boy, raising key questions. was it given to him?
dangerous. and disturbed. reporter: authorities suggest the immediate trouble starts november 26th, when james crumbley takes his 15-year-old son ethan to buy a sig sauer gun. along with the caption just got my new beauty today. no, no, legally, that s not his. reporter: the sheriff says by law the gun can t actually belong to the boy, raising key questions. was it given to him, was it allowed to be picked up and taken freely at his discretion? or was it stolen. reporter: november 27th, prosecutors say the mother jennifer posts mom and son day, testing out his new christmas present. november 29th, a teacher reports the boy is searching for ammunition on his cell phone in class. officials say the school called and emailed the mom. no response.