(CBS News) - No one saw the movie theater massacre coming, but maybe someone could have.
It turns out, days before the shooting, suspect James Holmes mailed a package to the University of Colorado-Denver/Anschutz Medical Campus where he had been a student.
The package was sent to a psychologist at the university, but the letter wasn't discovered until Monday.
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This was not unexpected. U.S. postal inspectors had been searching through the mailboxes near the suspect's home looking for letters and packages Holmes might have sent out. They didn't find any, but that's because the package had already been sent before the shooting.
On Monday afternoon, investigators scoured the mailroom at the university and found what they'd been searching for: a piece of mail from the suspect in the Aurora, Colo. shooting that killed 12 people and injured 58 at a midnight screening of the new Batman film last week.
Before opening it, the sheriff's bomb squad handled it with a robot and took an x-ray, just in case there were explosives inside.
Sources say the letter was from a pent-up Holmes to one of his professors. In it, he talked about shooting people and even included crude drawings of a gunman and his victims.
The letter arrived days before Friday's shooting, but had not been processed out of the mailroom.
Former FBI senior profiler Mary Ellen O'Toole said we may well see more letters from the alleged shooter.
"Particularly because of the complexity of this case and how much this person put into these two different crime scenes," O'Toole said. "They appear to want in my opinion a lot of credit for all their hard work."
The biggest question remains motive. Will the letter Holmes sent give any insight into that? Other cases, like the rambling video sent to a TV network by the Virginia Tech shooter have shown us that even when the suspects try to explain their actions, it rarely makes sense to anyone else.
"I can guarantee you, we will find it unsatisfying because there's nothing that this individual could say to us, the general public, to sit back and say now I understand why you did this," O'Toole said.
This was not random. Police had an investigative lead that put them in that mailroom and apparently the lead came indirectly from Holmes himself. Apparently sometime after his arrest he mentioned that a letter had gone to the school from him, and that's what they were looking for.
