The story involves a murder. A murder can be accomplished in a number of ways: with a gun or knife or poison or a rope or a candlestick in the dining room. That's what the game of Clue is all about. It is common in a murder to have a dead body because, I'm assuming, that it isn't always easy to get rid of the body unless there is a handy swamp or vat of acid. Buckets of cement are heavy, requiring assistance to lug the body off to the river.
And it is awkward to do the deed in public, which would make it handy to prove the guilt of the murderer. Circumstantial evidence is the best you can often do. Or the outright confession of the murderer - like the ends of the Perry Mason stories where the murderer can't stand it any more and breaks down and spills their guts. Seems a bit stretched to do that, however, especially since Erle Stanley Gardner did it so many times!
So if my intention was to involve a murder, the story needed to have a victim, a murderer, and a means of proof that wasn't a blurted out confession. Adding to that was the difficulty that I have never been a murderer or a policeman or detective and this story takes place in 1979 when there was no internet upon which to do research or DNA testing to prove guilt.
Such are the challenges of this tale. Challenges make for good stories, however - at least challenges that are well resolved.