Let's face it, security can never be 100% without the whole operation grinding to a halt. Look at the number of vehicles moving landside-airside every day.....caterers, cleaners, engineers, etc. etc. etc. To search every single toolbox, under every seat, etc. would grind an airport to a complete halt. How many hiding places are there on an average car?
Nevertheless, these guys should be prosecuted, as should the company concerned for failure to follow procedures before despatching the catering truck from base.