Can you really prove its a ruse? You have to prove beyond a reasonable doubt.

You don't actually, you just have to convince a jury. With motive, and this evidence, you are pretty dang likely.

Basically, jury nullification is a thing, and this is the same principle backward.

I know, but there are cases where something similar to "I just felt betting on his good health" have gotten someone acquitted.

It's important to remember that "beyond a reasonable doubt" means exactly that: no "reasonable" person would doubt it. (The definition of reasonable is left to the jury.)

Some people seem to think "beyond a reasonable doubt" means the same as "beyond any shadow of a doubt" - but they are very different standards!

You don't actually have to. You just have to convince 12 people that you did it. If this were so trivial to get away with people would you know actually be doing it.

Getting caught betting $500K against someone dying is likely going t turn up a lot more evidence of motive or other illegal activity.

Anyway, in real life a hit costs about $50K.