Yes many drains along these gutters.
Emirate: Aren't these grates adjacent to a drain though, so one wouldn't have to lift a grate but just kick it down the slot?
I also wonder why someone would dispose of evidence here, after all the other options on the road trip. Stinks of trying to set up a scenario like a robbery gone wrong. I reckon person went back to clean up evidence. LE are on it.
BUT, if the police were doing filming/3D modelling etc, they may have just been using the walkway entrance as a staging area so they didn't block people's houses, and the drains have nothing to do with this.
I still like drains anyway.