We have before us Mishnah 8 in the fourth chapter of Tractate Bava Kamma, in which we continue discussing the laws of the stoned ox - an animal that intentionally killed a Jew, and is sentenced to be put to death. The verse states: "Sakol yisakel hashor velo ye'achel et besaro" - the ox shall surely be stoned, and its meat shall not be eaten.
As a rule, the phrase "shall not be eaten" hints at a prohibition against deriving benefit as well - meaning that any form of benefit is forbidden - but not always. Our Mishnah teaches, as the Bartenura explains, that we must distinguish between two fundamental stages in the legal process of the ox:
Before the verdict: It is a positive mitzvah from the Torah to bring the animal to court and carry out the judicial process. A person who bypasses the system and hastens to slaughter his animal has nullified a positive mitzvah, but the animal is permitted to be eaten and he may eat from its meat, even though it is the animal that killed.
After the verdict: Once the ox's verdict has been finalized in court and it is set to be stoned, according to the Bartenura and most of the Rishonim, a prohibition against deriving benefit takes effect at that very moment - it is forbidden to derive any benefit from it whatsoever, including eating.
And if you will ask: The verse only stated "shall not be eaten," so from where do we know that additional restrictions apply? The Bartenura explains: Since it says, "the ox shall surely be stoned," the ox is stoned and becomes a neveilah (an unkosher carcass) that was not slaughtered properly, and it is obvious that it cannot be eaten. Rather, the verse must necessarily be adding that even if a person attempts to render the condemned ox kosher through a halachic slaughter - its meat still may not be eaten, and it is forbidden for benefit in any case.
According to the Bartenura, there are therefore only these two fundamental stages. Once the verdict is finalized and the ox is set to be stoned, it is already forbidden for benefit and ceases to be the owner's property: whoever was its owner is no longer its owner, and he has no monetary or financial rights to it whatsoever.
The text of the Mishnah:
"Shor shehu yotze lisakol vehikdisho be'alav - eino mukdash" - once the ox has been convicted of intentionally killing a person and is being taken out to be stoned, and its owner comes and consecrates it to the Holy Temple as consecrated property (hekdesh) - the consecration does not take effect, because it is no longer his property. Once the Torah forbade it for benefit, it took away all financial rights to it from the owner - or more accurately, the former owner.
"Shechato - besaro asur" - and if he preemptively slaughtered the ox before it was stoned, its meat is forbidden. As it is explicitly stated that it may not be eaten, and the verse comes to add that even if it was not stoned but was slaughtered with a valid, kosher slaughter - it is still forbidden.
"Ve'im ad shelo nigmar dino hikdisho be'alav - mukdash" - before the animal's verdict is finalized in court, before the prohibition of benefit takes effect, it is still considered property and belongs to its owner. Therefore, if its owner consecrates it and designates it for the Holy Temple - the consecration takes effect. Even though the owner is ostensibly bypassing the positive mitzvah of carrying out the stoning process, the animal is his and the consecration is valid.
To clarify a technical point: hekdesh comes in two fundamental types:
Kedushat haguf - inherent sanctity, which cannot be redeemed from the object.
Kedushat damim - external sanctity, where the monetary value is what is consecrated, and therefore the sanctity can be transferred from object to object through redemption.
Generally, one who consecrates an item fit to be offered on the Altar - kodshei mizbe'ach, which includes cows, goats, sheep, oil, wine, fine flour, frankincense, and wood - they are designated for the Holy Temple and acquire kedushat haguf. However, in our case, an ox that killed a person is unfit for a sacrifice, and therefore even when its owner consecrates it, it is only consecrated with kedushat damim, for bedek habayit - as property for the Holy Temple designated for use or liquidation, and not for being offered on the Altar. From this point, the gizbar, the treasurer in charge of the Holy Temple treasury, may take the animal, sell it at a public auction, and use its proceeds for another purpose, while the animal itself becomes completely non-sacred (chullin).
"Ve'im shechato - besaro mutar" - if the owner slaughtered the animal with a valid halachic slaughter before its verdict was finalized in court, its meat is permitted. Here too he has nullified a positive mitzvah, but since it was not yet convicted, it has not been forbidden for benefit, and its meat is permitted for him to eat.
In summary: In this Mishnah, we learned that the laws governing an ox to be stoned are divided into two stages. Before the verdict is finalized, the animal is still the property of its owner: its consecration takes effect - with monetary sanctity for Temple maintenance, since it is unfit for the altar - and if one slaughters it, even though he has nullified a positive commandment, its meat is permitted to be eaten. However, once its verdict has been finalized, it is forbidden to derive benefit from the ox, and it ceases to be the property of its owner: its consecration does not take effect, and even a proper slaughtering does not render its meat permitted.