Anyone could go to any military cemetery, then look at any stone and wonder who that person was. How is that a mystery?
Perhaps the "mystery" is how the pilot of a fighter plane can be shot down at the same time that he's being shot down as the rear gunner on a bomber crew of 6?
Quotes from above:
"Sgt Frederick Leonard Molteni .... was shot down as he flew his fighter plane..."
and
"RAF rear gunner Sgt Frederick ‘Leonard’ Molteni .... was killed with his five Wellington bomber crewmates..."
It is incorrect to call this a mystery. What is correct is to say that an author is seeking to know what the back story is about this and other downed RAF personnel. Journalists are as inept in the UK about military topics as they are here.