Gemara

(Mishnah): We do not begin capital cases on Erev Shabbos.

This is because if the majority are Mechayev, we must leave the Din overnight. We cannot give the verdict and execute on the next day, for Misas Beis Din does not override Shabbos. We cannot kill him on Sunday, for this is Inuy Din (delaying execution after the sentence)!

Bava Kama 90b (Beraisa): If a Tam ox killed and damaged, we judge it for death, but not to pay the damage. If it was Mu'ad, we judge it for money, and then for death. If first they judged it for death, they do not judge it for money.

Question: Even if they judged it for death, they should judge it for money!

Answer #1 (Rabanan): The Beraisa is Shimon ha'Teimani, who holds that Beis Din must evaluate whether the damager was apt to cause the damage. Once an ox was sentenced to stoning, we do not delay its Din to evaluate it.

Answer #2 (Rava): It is even like R. Akiva. The case is, he (or it) fled.

Question: If so, even if they didn't judge the ox to stone it, we cannot judge the damage in the owner's absence!

Answer: He fled after testimony was accepted.

Question: From where will the victim collect?

Answer: He collects from Ridiya (rental of the ox for plowing).

Question: If so, even regarding a Tam, we should first judge it to pay the damage through Ridiya, and then judge it to stone it!

Answer (Rav Mari brei d'Rav Kahana): This shows that Ridiya is not considered Gufo (the ox itself. A Tam pays only from Gufo.)

Mo'ed Katan 14b (Beraisa): We judge capital cases, lashes and monetary cases (during the festival).

Inference (Rav Yosef): If a party disobeys Beis Din, we excommunicate him. This shows that Niduy applies during the festival!

Question (Abaye): Perhaps we merely are Me'ayen (investigate). We must say so about capital cases, for if we kill, the judges would need to (fast, and) neglect Simchas Yom Tov to give a verdict!

Answer (Rav Yosef): If so, this is Inuy Din! Rather, they investigate the case in the morning, eat and drink during the day, and before sunset they give the verdict.

Avos (Mishnah 5:8): The sword comes to the world due to Inuy Din.

Rishonim

Rambam (Hilchos Sanhedrin 20:6): Delaying the verdict and extending clear matters in order to pain a party is Avel (injustice).

Rambam (Hilchos Nizkei Mamon 11:7): If a Tam ox killed, we judge it for death, but not for money (to pay the damage). If a Mu'ad killed, we judge it for money, and then for death. If they judged it for death, they judge it again for money.

Rambam (8): It pays from the value of the plowing it did after it was sentenced. Once it was sentenced to die, it has no owner to be liable to pay.

Rebuttal (Ra'avad): This is unlike the Gemara, and it is inconsistent. If (a sentenced Mu'ad ox works to pay its damage, and) we are not concerned for Inuy Din, then also if a Tam damaged, we should judge it for money after sentencing it! Rather, we are concerned for Inuy Din of an ox.

Magid Mishneh: The Rambam holds that after it was sentenced to die, if they judge it to pay, the owner need not pay from his own money. This is why the Gemara asked 'from where will the victim collect?' It answered that he collects from Ridiya; we are not concerned for Inuy Din. This is the conclusion. When the ox fled, there is no Ridiya. The Ra'avad explains like Rashi. There is no necessity (to favor their Perush).

Lechem Mishneh: After it was sentenced, it is as if it is not his ox, so we cannot obligate him for damage it did before sentencing! Even though Answer #1 (the Beraisa is Shimon ha'Teimani) is concerned for Inuy Din of an ox, Answer #2 is not. We judge for money after sentencing it, unless it fled. The Gemara asked, if when it did not flee we leave it to pay through Ridiya, we should judge also a Tam for money, let it work, and then judge it for death! We inferred that Ridiya is not Gufo. This Perush is difficult. If we answered that it fled, why do we say that we cannot judge the damage in the owner's absence? Perhaps this was not in the Rambam's text. Why did we suggest to judge a Tam to pay through Ridiya, and then judge it to stone it? We could even judge it for stoning first, and then for money, to collect from Ridiya! Also, the Rambam (Hilchos Chovel u'Mazik 1:18) rules like Shimon ha'Teimani! The Rambam must hold that the two answers argue with each other, and he rules like Answer #2.

Kesef Mishneh and Me'iri: We can say that the Rambam is concerned for Inuy Din of an ox. He did not say that we keep it alive to work. Rather, if it worked on the night after sentencing and the next day it was stoned, or if due to Ones Beis Din was unable to stone it for several days, the victim collects from Ridiya.

Tosfos (Mo'ed Katan 14b DH Nimtzeis): In Sanhedrin, we find that Inuy Din is only after it (the judgment) was left overnight after the verdict! We must say that indeed, Abaye meant that they will give a verdict.

Ritva (DH v'Omar): Rav Yosef said regarding capital cases that if we reach a verdict and delay execution, this is Inuy Din.

Rashi (35a DH Lidainei): Inuy does not apply before the final verdict, for the Nidon hopes for acquittal. After the final verdict, the Nidon waits to be executed, so this is Inuy Din.

Poskim

Shulchan Aruch (CM 17:11): Delaying the verdict and extending clear matters in order to pain a party is Avel.

Be'er ha'Golah: We learn from Avos 5:8 and Sanhedrin 35a.

Shach (14): We learn from Mo'ed Katan.

Igros Moshe (YD 1:159 DH u'Mah): Rashi (Mo'ed Katan 14b) connotes that the question of Inuy Din refers to monetary cases. (Note: Rav Yosef wanted to teach about Niduy, which applies to monetary cases, and Rashi did not specify that the question about Inuy Din applies to capital cases - PF) We must say so, for if Inuy did not apply to monetary cases, we could postpone the verdict and not need to excommunicate (and Rav Yosef has no proof)! Perhaps this answers Tosfos' question. However, if we judge monetary cases with a verdict, the same applies to capital cases (the Beraisa taught them together), therefore, we needed to say that they investigate in the morning... Be'er ha'Golah says that we learn from Sanhedrin 35a. There it does not discuss monetary cases!

Levush (13:1,2): The parties need not agree on the third judge, lest they be unable to agree, and this is Inuy for the claimant. We write which judges they chose to avoid retraction and Inuy Din.

Levush (16:2): When it is possible to bring a proof in a short time, we do not delay the Din without need, even if no one will lose, for this is Inuy Din.

Levush (109:3): Some say that if Beis Din sold land at a time when buyers were scarce and this cheapened the land, e.g. at a time of a plague or war, what they did stands. We do not say that they should have waited until the plague stops or war subsides, for Beis Din must do Din for a claimant when he comes, and it is Inuy Din to defer him. Some disagree and say that since it is a nationwide affliction, this is not Inuy Din.

Pischei Teshuvah (YD 242:9): Mishnas Chachamim (Hilchos De'os Lav 7) asked whether Inuy Din applies only to monetary laws, or if even in Hora'os of Isur v'Heter, i.e. once the ruling is clear, one may not delay it and say 'return later.' He brings the Shlah, who says that it applies to Hora'os just like to monetary laws. Mishnas Chachamim says that according to Rashi, who says that "Lo Sa'anun" forbids Inuy of anyone, it applies to Hora'ah. According to the Rambam, this verse applies only to widows and orphans. "Lo Sa'asu Avel ba'Mishpat" forbids Inuy of everyone. If so, we can distinguish Mishpatim (monetary laws) from Hora'ah. If a ruling would permit a woman to her husband, all forbid delaying it.