I may be recalling the wrong accident, someone please correct me if I am, but if IIRC, I have a vague recollection this accident involved a day when there was a thin layer of sea fog as well as multiple layers of low cloud.
They had been chasing various targets climbing and descending through the layers and flew into the sea chasing down a target flying just above the fog.
The supposition being that they lost SA and thought the fog layer was just another cloud layer and descended into it.