That makes me suspect he had other plans originally.
Why is NBC saying ‘timestamped’ instead of ‘postmarked’?
Could be. It may have been a twisted attempt to shelter his parents or his ID.
Seems he initially shot the two to death, wandered over to his dorm room, knowing the would eventually get him for the first murders, he apparently has plenty of time, he puts together a package of photos, videos and writings, drops it in the mail, loads up his weapons, extra clips and decides to go out in a bloody murderous blaze.
There is no doubt, this guy had planned something for a long time..
I think you are right, after he chained the doors and killed all those people, he was going to drop the guns make a run for it but couldn’t get out because he lost the keys so he blew his demented brain out. One of those ‘Doh’ moments. s/off