Sorry but I disagree. As soon as the cops pounced on him Thompson would know he screwed-up and the LAST thing he'd do is rat out his boss about "misinforming him".
You are certainly entitled to your opinion, but I see little to no likelihood that Webb gave it to him and said he could take it in. Why would he? I'm sorry, I can't hang my hat on "they just think they are above the law" or the ridiculous notion that Webb sent him in there to kill "political enemies" as the one poster said - when the most logical explanation is that the aide picked up the wrong bag.