Had a similar experience a few years ago on a very nice buck. He had no obvious signs of injury, and we suspected he had been hit by a car or broke his back fighting with another buck.
We called the Sherriff's office and asked if we could put him out of his misery and they said no. Said that they were closer than the nearest game warden and we must wait until he arrived. Around an hour later, he got to the farm, and we took him out to the buck. He shot it point blank with his .40 cal sidearm at point blank range through the lungs and began writing a salvage tag. A few minutes later, the deer was still very much alive, and he shot it twice more through the lungs at PBR. The deer kicked for a few more minutes and finally let out one long last breath.
The whole thing was extremely tough to watch, and the amount of unnecessary suffering was sad. He finished writing the salvage tag and we gutted and took the buck home. I don't know what kind of ammo the Sherriff's office was issued at that time, but none of the rounds expanded on the buck, and he had 3 caliber sized entry/exit wounds.