Was this the an attempt to assassinate Churchill? An apparent attempt to assassinate Winston Churchill in the air. On June 1, 1943 the BOAC DC-3 commercial airliner Howard was aboard was shot down by the German Luftwaffe over the Bay of Biscay, the portion of the Atlantic Ocean immediately north of Spain and immediately west of France. There were 17 persons on board, 13 passengers and 4 crewmen. None survived. http://www.law.uga.edu/academics/profiles/dwilkes_more/other_1ashley.html
I saw a documentary asking this very question about 2 years ago. I can't remember all the details but the conclusions were pretty inconclusive.