If all you’re looking for is motive, then I will point out that the majority of the US government is composed of old men. They’re also primarily wealthy, and have probably the best health plan in the country. I have no idea how many congresscritters or other high ranking washington types have pacemakers, but I’m sure it’s more than a few. And with their resources, I’m sure they all have the best and newest. In other words, if you had to pick a group of people most at risk for an attack of this kind, it just happens to be the same group that has the ability to pull off a “died under mysterious circumstances” to prevent it.
That’s still not proof by any means, but as a conspiracy theory, it is definitely plausible.