Sefer HaChinuch ספר החינוך

To not kill someone liable before he is brought to justice: That we were prevented not to kill the sinner when we see him doing a sinful act for which he is liable the death penalty, before we bring him to court. Rather, we are obligated to bring him before the court and we bring witnesses in front of [the judges] and they sentence him to what he is liable, as it is stated (Numbers 35:12), “and the killer shall not die before his standing, etc.” And the language of the Mekhilta (Sifrei Zuta on Numbers 35:12) is “Perhaps they should kill him from when he killed or was adulterous? [Hence] we learn to say, ‘and the killer shall not die before his standing, etc.’” And even if the Great Court saw him kill, they would all be witnesses and take their testimony to another court to judge him. And they also said in Mekhilta (Sifrei Zuta on Numbers 35:12), “Behold, a community that saw one kill a soul, perhaps they should kill him before he stands in court? [Hence] we learn to say, ‘and the killer shall not die before his standing.’”

It is from the roots of the commandment [that] since the matter of capital punishment is a very weighty thing (Rosh Hashanah 26a) which requires the greatest of precision, and the community has been commanded to save the accused with everything that is fit to save him for his sake — not that they pervert the judgment in order to save him, God forbid, and like they, may their memory be blessed, expounded (Rosh Hashanah 26a, connecting the two phrases in Numbers 35:24-25), “And the community shall judge, And the community shall save,” meaning to say that they need to search for his merit and if he has a merit, they should save him, and if not, he should be killed — therefore, we were warned that the judgment should at the very least be brought before the court. And the witnesses that saw the thing with their eyes should never judge him, as maybe from their seeing the matter, they will not be able to search for his merit, as their hearts will arouse them to render him guilty no matter what.

From the laws of the commandment is, for example, that which they, may their memory be blessed, said (Sanhedrin 73b) that what are these things speaking about that we do not kill the sinner until we bring him to court; when he went and did the sin, but [with] one who is pursuing his fellow to kill him or after a betrothed maiden and they warned him but he did not stop pursuing, even though he did not [formally] accept the warning, we are obligated to kill him and we are warned about it, and as we will write with God’s help at the end of the Order of Ki Tetseh in the warning of “You shall cut off her hand; show no pity” (Sefer HaChinukh 600). And the rest of its details are in Tractate Makkot.

And this commandment is practiced by males and females at all times, as we are commanded not to kill any sinner — and even though we saw him doing an act that would make him liable for the death penalty in court. And at the time of the [Temple], we are obligated to bring him to court and they judge him. And one who transgresses this and kills the sinner before he comes to the court — even if his judgment was that he would be deemed guilty in court — the ruling for the one who killed him would be like the ruling of a murderer, and he would be killed for it at the time of the [Temple] if there were witnesses.