I agree with the theory that this was an inside job, probably by the company itself, for the purposes of insurance fraud, and that Dale was not involved but rather set up as the fall guy.
I note how, in the original Unsolved Mysteries broadcast, C. Dale Parry, the Personnel Manager, starts out by coolly calling Dale a "marginal employee" and a "slow worker" with whom they'd had "some problems occasionally." Patrick Foley, the former Personnel Manager, states his belief that Dale looked at the camera to flaunt his crime, and adds that Dale was "not a happy person at the time of his death" because of a recent $5,000–$7,000 pay cut.
Now these things may be true, but they strike me as really insensitive things to say on a broadcast that they know Dale's family is most likely going to hear and even participate in. Maybe Parry and Foley provided specific incidents to show that Dale was "marginal," "slow," and "not happy," and that these were edited out of the broadcast. But you'd think that after 30+ years, some of those incidents would've emerged but, as far as I know, none have. So this leads me to believe that management already didn't like Dale and were intentionally trying to paint him as a disgruntled employee.
The night of Dale's disappearance, a new employee conveniently failed to check in on Dale every hour on the hour. Arrin Stoner uploaded
the security video to his YouTube channel (07:38–12:00), and you can clearly see the time stamp is around 10:45:52 to 10:46:00—pretty much at the beginning of Dale's shift. I can understand if the new employee missed one or two hours, but Dale was supposed to leave at 7 am, so you're saying the employee missed eight check-ins? I'm not buying it.
And for that reason, I think Dale looking at the camera was a silent cry for help. Unfortunately the footage has degraded so much by now that we can't see his facial expression. But I believe Dale knew there were 15 minutes left in the hour, and was betting on that first check-in which never came. Maybe that's why he complied with the intruder and appeared calm because he figured this was only temporary, and that help would be coming soon.
Management themselves say whoever stole the platinum knew the layout of the place, and in the recreation of the video, the intruder alone is sawing off platinum, so it's not like Dale was giving him a tour. The intruder knew exactly where to go of his own accord. The fact that the company was losing money (hence Dale's pay cut) makes me suspect them of orchestrating this theft and pinning it on Dale.