Took the dog for a wander in the park 6pm and there was a man head to toe in black clothes, including a black scarf wrapped around the face, hiding against the wall where the path leads behind the tennis courts.
He'd been there completely still for about ten minutes watching people walking through the park. I made a point of knowing he was there and gesticulated to another dog walker who came into the park, at which point the guy sprinted off.
I suspect he was waiting for someone to walk through on their phone and do a grab-and-run or waiting for a dog walker to enter the bit behind the tennis court.
A security guard (with annoyingly loud dog) parks in a van immediately behind the tennis courts each night from 8pm to 8am. He's guarding the offices behind which were broken into last year. Hopefully will deter this guy later in the evening.