They’ve stopped executions because the drugs were two weeks beyond their expiration date, and were therefore assumed to be no longer effective. Nothing could be further from the truth, but it was enough for a progressive judge to halt the execution.
My suggestion is to use the exact same method for the execution as the convicted murderer used on his victim. Strangulation? The death by hanging. Shot his victim? Then shoot the sonny beach. Poisoned his victim, then by all means chemical execution without palliatives to ameliorate the symptoms. Stabbed? Ditto. The basic Eye for an Eye approach that might serve to dissuade future murderers from killing.
Not completely certain that this is the murderer, i.e. the DNA evidence proves he is the killer? Then use the veal prison approach proposed by a friend of mine: Take an island in the pacific somewhere, provide a cabin, a 100‘ chain connected to a heavy duty stake in concrete in the middle and to the convict, a very deep hole for a latrine, and put the convict there, alone. Drop food, water, and reading material, weekly from a helicopter. No TV, no internet, no sports. He can wander around in a 200” diameter circle, seeing, speaking to no one, sending/receiving mail through the helicopter. He can’t hurt anyone, can’t kill anyone, can’t harm society. Serves his sentence there. If exonerating evidence appears, he hasn’t been executed wrongly.