Additional thoughts:
Forums like operatorchan are all ABOUT bravado, they are places where many go who feel somehow powerless in the real world and they talk a big game online [like many comments sections, ahem]. 4chan is a good example as well. If you reveal you are a female on forums like these, literally the next reply will be a vulgar request for some naked photos, and there is a high chance of your social networking sites getting hacked. I've seen it happen.
When reading what SMD writes on these forums, it's obvious he is trying to project the person he wishes himself to be, because we all know how the reality of his personality and behavior conflicts with this tough guy act he puts on in his posts.
It's pathetic, but not unusual.
He wouldn't bust a grape in a fruit fight.
But he would spend a lot of time fantasizing, planning ways to take someone who is unsuspecting and unarmed [because he is a coward], and with some luck he could pull it off. Looks like he did.
If he had planned this crime for a while, I wouldn't be surprised if he anticipated the possibility of his posts being tracked eventually if he were ever suspected, so he threw in some minor foils here and there, IMO.
I do believe one thing he said, which is that he wanted a better life than that of his sister. I'm pleased to say he won't be getting it, most likely.