Yes, i'm aware - there are federal murder statutes, but they are mostly about murder of federal police officers, hate crime murders, etc.

However, murder for hire is also federal crime - see 18 USC 1958 and the DOJ CRM on this: https://www.justice.gov/archives/jm/criminal-resource-manual...

So depending on the pardon text and interpretation, he may or may not be chargeable with this statute still federally.

I agree this has zero effect on charging him at the state level, and most states do not have statute of limitations on these types of crimes (or they are very long)