Exodus 21:29

But if the ox (had been wont) to gore yesterday and before, and it had been attested before his owner three times, and he (had neglected) to restrain him, the ox, when he killeth man or woman, shall be stoned, and his master also shall die with a death sent upon him from heaven.

AND ITS OWNER SHALL BE PUT TO DEATH. Our Rabbis have received by Tradition that this death means by the hand of Heaven. Similar cases are these verses: and the common man that draweth nigh shall be put to death; and they die therein, if they profane it.
I have noticed that where the Torah speaks of those liable to be put to death by the court, it does not mention just yumoth (he shall be put to death), but always says, moth yumoth (he shall surely be put to death). Do not object to this rule from the verse, and he that killeth a man ‘yumoth’ (shall be put to death),! or from the verse about the Sabbath, (further 35:2), and his punishment is death by the court! or a prophet who misleads, (Deuteronomy 13:6), and there too his punishment is by the court (Sanhedrin 84 a). for in each of these cases He has already clearly explained elsewhere about them [that they are liable to death by the court, by using the phrase: moth yumoth]..
Now I do not know the reason for Onkelos’ rendering yumoth as yithk’teil [“he shall be killed”, which indicates that his death is to be by the court, instead of by the hand of Heaven]. Perhaps his intention is to state that the owner, [who had been previously warned that his ox had gored three times, but still did not guard it, so that it went out and killed a man or woman], deserves to be put to death, but is instead made liable to the payment of a ransom. Or perhaps Onkelos means to explain that that which Scripture states, and its owner also shall be put to death means that the owner will perish in a similar manner to that by which the gored person was killed, for his day shall come to die, or he shall go down into battle, and be swept away; the Eternal will not hold him guiltless. Thus Onkelos wanted to teach us that the owner of the ox is liable, according to the view of Heaven, to die by the hand of a killer, and not by a natural death, something like it is said, and I will kill you with the sword. In the verse, and the common man that draweth nigh shall be put to death, Onkelos also translated yumoth as yithk’teil [“he shall be killed,” indicating that his death is to be by the court], because he agrees with the opinion of Rabbi Akiba who said that a non-priest who performed the Divine service in the Sanctuary is put to death by strangulation.

וגם בעליו יומת, by heavenly forces as opposed to by human tribunal. If the owner did make restitution of monetary kind he is not guilty vis a vis heaven either.

וגם בעליו יומת. A reference to judgment by heaven which will be exacted from the guilty party if we cannot convict him due to lack of witnesses.

ואם שור נגח הוא, “but if that ox had had a history of goring people, (and its owner had not taken proper precautions);“ The Talmud, tractate Baba Kamma folio 23, relates a dispute between two scholars, Abbaye and Rava whether the term נגח applies to an ox that already gored twice or whether even after having gored once, that animal belongs to the category of being potential a killer, and its owner being guilty of not having protected potential victims properly. The subject of their dispute is the meaning of the word תמול, usually understood to mean “yesterday.” According to the former scholar, even a single incident of goring suffices for the ox to be categorised as dangerous, and the prefix מ i.e. מתמול, would refer to the second offense by that ox, so that the words ולא ישמרנו, “and its owner did not watch it adequately,” would make him liable to stoning only the fourth time whereas according to the second scholar, basing himself on the word שלשום, “day before yesterday,” that ox’s status did not change from harmless to dangerous until after it had gored three times. According to Rava, the words ולא ישמרנו, would then mean that only after a third such occurrence did this ox change its category, and its owner became guilty on an additional count According to the Talmud in tractate Baba batra, folio 28, such an ox is subject to stoning only after it has gored the fourth time. seems therefore that Abaye found four sources in the Torah’s text supporting his view whereas Rava found only three. If you were to ask what difference this makes, [after all we do not decide questions of halachah on the written text of the Torah, but use it only as broad hints, Ed.] Rabbi Ezra hanavi claims that there is a difference. The difference would be if the fourth goring had occurred on the same day as the third goring. According to Abbaye, if the last goring would have occurred on the same day as the previous one, the owner as well as his ox would not be held liable for the additional negligence, as the owner on a day when his ox was bad-tempered had not yet had time to place him under secure restraint.