What is to be found in the grid is delightful and very clever. Having found the perpetrators, I left the puzzle and went out for some exercise. It was during that time I thought, "I wonder if..." When I returned to the puzzle and looked more closely at the grid I saw the icing on the cake.
The device used in the last stages of the puzzle is one I detest, it is so mind-numbingly tedious (I'd be happy if it were banned!). However, in this case it was possible to short-circuit most of the tedium using ODQ's keyword index.
It was a pity that there were so many entries with no unchecked letters (20, I think). That, coupled with some very easy clues, made filling the grid abnormally quick. I had the first four rows of the grid filled within three minutes. Admittedly it got a bit harder after that, and there were a lot of clues, so some may be grateful that they weren't hard.