How many innocent people are murdered a year?

This is an oddly-based question. What definition of "innocent" are you using?

Do you mean by methods of capital punishment? It is not clear that we could ever know whether someone really committed a crime, unless we have an unsolicited, signed confession from the real criminal.

We may also think of "innocent people" as bystanders, in which case, there may not be exact statistics.

We also need a geographic specification: worldwide? In the US?