Reporting a potentially dangerous situation

Whist walking and sitting in one of the fine establishments enjoying a beer on the sea front, I observed a garbage man emptying the many small bins located up and down the road - 2 nights in a row.

Each time this single person drove to a bin, got out and for more than 5 minutes; picked up the trash around ( they were overflowing) and placed this in the back and then emptied the bin into the back of the truck. Whats the problem??? He was doing his job - yes, a little slowly but this is Spain. The problem was that whist he was behind the vehicle with his mind on picking up the trash on the ground and emptying the garbage bin, talking to tourists or locals, looking at his phone & looking at the girls; his 3+ ton truck was sitting there with the engine running - totally unoccupied. This was the day after some Spanish residences "hired" a van to drive thru people in Barcelona and a year and a month from the same situation in Nice, France. Seems to me in Benidorm that somebody with this modus operandi for an attack just has to get into this trucks cab and take off thru the crowds that walk up and down the boardwalk every night.

This situation could be easily stopped by the driver turning off the engine and depositing his keys in his pocket(s). Is this a valid argument/ potential danger to you? This situation could not even be a so called terrorist situation but a drunk tourist having a "joy ride" with dangerous consequences for him/herself and the many people strolling down the water front. This could easily be stopped by my first sentence in this paragraph.

Who can I report this observation to?? Is it worth it? Is it a valid argument that would be taken seriously?

Thanks...