I read about one case much like that.

A TSA agent stole from a suitcase. The victim was friends with the local sheriff, who somehow got a tape of the inspection/theft, clearly showing the theft. He filed charges.

The TSA went to the judge and told him that the tape would reveal their "secret" methods of searching suitcases, and they wanted it suppressed. The judge refused to allow it as evidence, and ordered it returned to the TSA. Without it, the crook couldn't be convicted. Nor did the TSA reimburse the victim (since he couldn't get his stuff back from the crook).

Of course, the TSA's claim was nonsense; their "secret" methods were known to at least one crook, who would doubtless be willing to sell them for a very small price.

(Had I been involved, there would have been a copy of the tape on YouTube before the trial, so that the judge would have had no reason to suppress it.)