If an ox was being taken out to the stoning, it was finished, it's judgment. Or even if you're talking about a situation where it was sentenced to death but wasn't taken out to be stoned yet, after it was sentenced to death, until it was actually put to death. And the owner consecrated it to the Beit HaMikdash and Hekdesh (consecration). It's not consecrated. It doesn't take on that holiness. It's not considered to be the property of the Baal HaShor (owner of the ox) anymore. It's not owned by that owner at that point in time. An animal that's been sentenced to death is Asur BeHana'ah, can't benefit in any way; the owner can't benefit from that animal. So, since the owner can't benefit from it, the owner doesn't really have any rights of ownership over it. It's worth nothing to the owner. And therefore, it can't be consecrated. It can't be dedicated to the Beit HaMikdash. And therefore, the owner killed and slaughtered that animal because it was not considered to be the property before it was actually stoned. The meat is forbidden because once an animal has been sentenced to death, the Torah does not allow that person to have any benefit from that animal.
If the owner, though, before the judgment was fully decided, dedicated this animal to the Beit HaMikdash, then the animal is consecrated because it was still within his ownership. He did something wrong. He wasn't allowed to do that, but it's still considered to be the property of the Beit HaMikdash. After the judgment was given on it, that animal has to be put to death. So the Beit HaMikdash can't really take and do anything with it, and it also can't be killed because it's property of the Beit HaMikdash, so that animal is sort of stuck in limbo.
If the animal was slaughtered before the judgment was decided, then the meat of that animal is allowed to be eaten because the Isur of Hana'ah (prohibition of benefit) doesn't come into play until the animal is actually sentenced. The person doing something wrong over here, he's an avaryan, he's a sinner, because he's not allowed to take the animal that killed somebody and go slaughter it. It's the obligation of his owner to go take it to the Beit Din (rabbinical court) and have it judged, so he did something wrong, but on a technical level, the meat is still allowed to be consumed.