The Torah teaches us what happens in a case when two witnesses testify against someone and say that he sinned, and afterward two other witnesses come and say their claim is utterly unfounded since they original witnesses were in another place at the time they claim to have seen the transgression.
"They say to them: how is it you testify for you were with us on that day in such-and-such a place. So these [the first witnesses] are zomemim, conspiring or false, and are killed by the [testimony] of their mouths." (Mishnah Makot 1,4)
The punishment of witnesses that have been found to have conspired, eidim zomemim, is that the punishment they sought to inflict on another through their false testimony is instead inflicted on them. "And you will do to him what he conspired to do to his brother." (Devarim 19, 19) The testimony of the second set of witnesses proves that the first set devised a plot designed to set the wheels of the justice system in motion with the goal of killing the defendent. (Obviously there are possibilities that don't involve capital punishment and are not as harsh, like payment of money owed, fines, or lashes.)
The law of eidim zomemim is an unusual one. It does not apply in every case where people bear false witness; it only applies if a second set of witnesses completely negates the first testimony and proves that the first set's claim is impossible, since they could not have witnessed the event at all. This is not the case if the content of the first testimony is proven false, for instance, if they testify that the murder was performed by gun instead of knife. In such a case the second witnesses are seen as eidim makchishim, witnesses who refute the testimony of the first set, and not as eidim mezimim, witnesses who make the first set into eidim zomemim. In the case of eidim makchishim the first set of witnesses become false witnesses, but they are not considered "zomemim," and they do not recieve the punishment the victim of their false testimony would have recieved.
According to Chazal the law of eidim zomemim only goes into effect if the subject of the first testimony has not yet been punished based on their testimony. If the punishment has been carried out and the accused put to death, then the eidim zomemim are not killed. The Sadducees disagreed with Chazal. They held that if the accused had been put to death on the basis of the first set's testimony then the eidim zomemim are killed in accordance with the law of "nefesh tachat nefesh," "a life for a life." But if the original judgment had not yet been carried out then they are not killed. (Mishnah Makot 1, 6)
These two opinions disagree about a very basic queestion: why are eidim zomemim punished? According to Chazal they are punished because of their intention, because they wanted to cause an innocent person harm. According to the Saducees they are punished because of the action that followed as a result of their testimony, because they did cause injury to an innocent person.
The two approaches also differntiate between different results. How many people are to die as a result of this conspiracy? According to the Sadducees both the innocent man and the people who conspired against him die. According to the Talmudic sages the witnesses only die if their plan does not succeed. Chazal's opinion makes sense if we understand that it flows from their mercy, they are trying to put an end to the bloodshed.
The Sadducees, on the other hand, seem to asssume that the foundation of this law is the concept of midah k'neged midah, measure for measure. They seek justice. If someone plotted to kill another but was not successful there is no justification for killing them. If we judge the witnesses' actions by the results we could say "no harm, no foul," they didn't actually do anything and so they do not deserve to be punished. Moreover, Torah law commands us to kill murderers, even though it causes more bloodshed.
The gulf between these two approaches seems even greater in light of the strict code the Beit Din must follow. According to both opinions the formal law requires the Beit Din to accept the testiomony of the two witnesses, and then to accept the testimony of the next set of witnesses which is mezimah the first set, and then if another pair of witnesses comes which is mezimah the second set they must accept those too, and on and on ad infinitum, "for they say the latter is always true until they are proven false (yazomu)." (Rabbeinu Chananel, Makot 5, 1)
This commonality reveals another layer in the dispute between Chazal and the Sadducees. They diagree as to the level of responsibility the Beit Din bears. According to the Sadducees punishments can continue ad infinitum until all guilty parties are brought to justice. This approach believes that the wheels of justice must continue to turn, and punish those who started them rolling. The Beit Din in this case is an ax in the hands of the murderer; they are not guily, the people who abused the system are the guilty ones. Chazal, on the other hand, place the blame squarely on the shoulders of the Beit Din, which they do not think should be considered a tool in anyone's hands. After the first mistake is made and someone has already been punished the sages put an end to the process. They do not seek to pawn off the responsibility for the miscarriage of justice, instead the guilt lingers, hanging over the heads of the judges on the Beit Din and echoing through its chambers. The judges and the decision of the court are the guilty parties; it is their mistake that caused the death of an innocent person.
Tannaitic sources understand that sometimes the court will make mistakes. There are sources that address what happens in such cases. There is a discussion about what punishment a Beit Din recieves if they mistakenly impose a punishment. "The messenger of a Beit Din that gives lashes with the Beit Din's permission is exiled." (Tosefta Makot 2, 5) Yet another source excuses the messenger of the Beit Din from damages even when it is clear that he should pay according to the letter of the law, "mipnei tikkun olam" "for the proper functioning of the world." (Tosefta Gittin 3, 8) People who hold jobs that serve the needs of the community have to have a certain level of immunity, otherwise no one would take those jobs.
Yet after studying the position of Chazal and the formulaic laws that govern the case of eidim zomemim, one gets the feeling that the situation has gotten out of hand, like Frankenstein's monster turning on its creator, or a golem that rebels. Perhaps this is the reason that the topic of eidim zomemim is often presented as a monster swallowing everything around him, and used as a source of intellectual amusement for Torah scholars.
Using an internal language understood mainly by learned people they play with the concepts surrounding this law to probe its depth and breadth. For example, the Minchat Chinuch brings the case of two people who came to testify that they saw the new moon for Rosh Chodesh Nissan. Afterward two adolescents who were born on Rosh Chodesh Nissan 13 years previously arrive to contradict the testimony of the first and contend "you were with us." These two adolescents only turn 13 and therefore are only eligible to testify if the testimony of the first witnesses is accepted. Yet once they contradict the initial testimony Rosh Chodesh Nissan is pushed off and they indvertantly disqualify themselves from testifying. (Minchat Chinuch Mitzvah 94, Kidush Hachodesh.)
Israeli Supreme Court Justice Moshe Zilburg brought another pilpul of the Gerrer Rebbe, the author of Chidushei HaRim, on the same subject. His idea is based on the law that the testimony of any witnesses who cannot be made into eidim zomemim is inadmissable. The Chidushei HaRim claimed that if we really thought things through then all testimony could be considered eidut shelo nnitan lhazama, testimony that cannot be invalidated in this way. As proof he gave the following logical argument:
We believe the first group of witnesses because a second group can come and make them eidim zomemim. And we believe the second set because a third set can come and do the same to them. This is why we also believe the third set, and the forth set, and on and on. But eventually we will run out of witnesses and the last group of witnesses will not be able to be eidim zomemim. This nullifies the admissability of their testimony, which in turn nullifies the testimony of the witnesses they cannot bear witness against, and so on and so forth up the chain, each testimony is ineligeable until we disqualify the first group of witnesses. ('Kach Darko Shel Talmud,' pg. 126)
These intellectual gymnastics highlight the power the mechanism of eidim zomemim has on the entire system of testimony. They paint the picture of a tool that has an inner dynamism all its own.
However there are other ways to understand the issue. Ramban preceeded these scholars and he came to the defense of the Beit Din, concluding that they never truly make a mistake. He claimed that if they killed someone that seemed is later found innocent based on testimony that only comes to light afterward, such a death must be the result of a heavenly decree. For "if he was innocent (tzaddik) God would not have left him in their hands."
"For God would not allow the pious judges that stand before Him to spill innocent blood, for judgment is God's, 'they judge in the midst of God.' And all this is a great advantage that Israelite judges have, with the promise that God is in agreement with their decision in matters of justice. And this is the reason [for the verse] 'and two people that have the dispute will stand before Elohim.' (verse 17) (The word Elohim has a numbe of meanings, and in this case could mean either God or the judge.) For they stand before God when they come before the priests and judges, and He will guide them on the true course..." (Ramban Devarim 19, 19)
The Ramban introduces a new element into this conversation, the religious understanding that the Beit Din is not merely a human court that is judged by the rules that apply to humanity and our limitations. The Beit Din is an arm, one of the arms of God; it is the representative of His reign over this wold, and it works according to the rules He laid out. Based on this idea one could understand that the Beit Din is not free to act in a manneer that is not God's will. Much like a person's arm only moves and acts according to their will. While it may seem that the Beit Din is empowered by a formal mechanism, the internal dynamics that seem to run on infinitely are really a revelation of God's Shechinah, God's presence in the judicial process. On the same token the Beit Din is not merely a golem, for better or for worse it has the power to create.