the boy returns to class. his parents leave. >> we have to believe he had the weapon either on his person, in his backpack, or somewhere secreted in that travel route. >> reporter: just before 1:00 p.m., investigators say ethan goes into a bathroom with his backpack, comes out gun in hand, firing. four students are killed, seven wounded. he is apprehended minutes later. at 1:22, officials say, his mother texts, ethan, don't do it. his father -- >> upon hearing that there was an active shooter on that day, mr. crumbley drove straight to his home to look for his gun. >> reporter: 1:37, the dad calls 911 to report his gun missing and to say his son may be involved, but in the wake of the note just hours before the violence, officials thought there should have been more. >> the notion that a parent could read those words and also know that their son had access to a deadly weapon that they