Maybe they were both citizens of California, the guy didn't die and sued him in a California court (which applied the law of Nevada, of course, using vested rights theory). The victim won a judgment but Cash didn't pay up so the CA courts put him in jail for contempt.
Or maybe he shot him in Reno, but the guy died much later in CA and the CA courts thought, for some reason, that that was when the actual crime was committed.
Whaddaya think, counselor?