So this is another reason why the burden of proof is on the person presenting the pictures of the Deep Blue "treasure"
Your statements are easily proven wrong by simple logical reasoning. Read any LSAT logical reasoning book if you don't believe me.
This is invalid logic because the fact that no computer record exists does not mean that the person is not a convicted felon. You've made a huge leap of logic. The fact that there is no computer record means nothing more than there was no computer record of a felony for a particular person on the day the record was checked. It isn't proof that the person was not a felon. Maybe the computer records hadn't been updated, maybe the court hadn't entered the record into the database, maybe the outstanding warrant had already been executed, etc. And yes, these things happen all the time in police work.
Your statement is analogous to saying that you can prove that a regulated entity has committed no regulatory violations because they were examined by regulatory examiners on multiple occasions and no regulatory violations were found. Again, that is an invalid leap of logic. That means nothing other than the fact that the examiners did not record any violations. They may have found violations and not recorded them or they just may not have been able to find violations. Madoff was examined on multiple occasions and was never found to be running a Ponzi scheme. He confessed!
That's not proof. Maybe they were diving on a day they weren't being watched or before you started watching or after you stopped watching or at night when you couldn't see them or maybe they farmed out the business to another captain...the point is that watching them for a few days/weeks is not "proof" of anything.