Question: What is the source that his confession atoned for him?

Answer: It says "u'Vnei Zerach Zimri v'Eisan..." R. Yehoshua ben Levi said, Zimri is Achan. [He is called Zimri] because he did a [terrible] act like Zimri;

R. Shmuel bar Nachman said, Heiman is Achan. [He is called Heiman] because he said "Amnah Anochi Chatasi";

Why does it say "Kulam Chamishah" - do I not know that they are five [listed in the verse]!? Rather, this teaches that even Achan (who is among the five, both according to R. Yehoshua ben Levi and Shmuel bar Nachman, has a share in the world to come).

A case occurred in which one was being taken to execution. They told him to say 'my death should be a Kaparah for all my sins.' He said 'my death should be a Kaparah for all my sins except for this - if I did it, do not pardon me, and Beis Din of Yisrael should be innocent';

When word came to Chachamim, their eyes flowed [with tears]. They said "it is impossible to return him, for if so, there is no end to the matter (everyone will say so)! Rather, [if he is innocent, liability for] his blood hangs on the neck of the witnesses."

(R. Yehudah ben Tabai): I should [not] see the consolation [of Tziyon] if I did not kill an Ed Zomem [to refute the Tzedukim], for they say [that Edim Zomemin are not killed] unless [the defendant] was killed, for it says "Nefesh Tachas Nefesh."

Shimon ben Shetach: I should see consolation if it is not considered as if you spilled innocent blood! (We kill an Ed Zomem only if all the witnesses are Huzam. The Ramban and Ritva in Makos (5b) say that the witness was Chayav Misah for another Aveirah. The Ramban in Chulin (7a) says that he was Chayav Misah to Shamayim, and Hash-m arranged that he die through R. Yehudah ben Tabai.)

At that time, R. Yehudah ben Tabai accepted that he will rule only in front of Shimon ben Shetach.

Shimon ben Shetach's hands were hot [to judge Resha'im. He sentenced 80 witches in one day]. A band of scoffers (their relatives) said "let us take counsel to testify about his son, and kill him!" They testified about him, and his final verdict was to be killed.

When he was taken out to be executed, [the witnesses] said to [Shimon] "we are liars." He wanted to return [his son to try to repeal the verdict. Even though witnesses are not believed to retract, perhaps they can be Huzam.]

[His son] said "father - if you want salvation to come [to Yisrael through you], make me like a porch [that everyone tramples on it. It sanctifies Hash-m's name that you did not have mercy on your son to try to save him]."

A case occurred with a Chasid who was going on the road. He saw two men having Bi'ah with a dog. They said "we know that this man is a Chasid. He will testify about us, and our master David will kill us. (A king may pass sentence without two witnesses.) Let us go first and testify about him (that he had Bi'ah with a dog)!

They testified about him, and his final verdict was to be killed. This is what David said [after he learned the truth] "Hatzilah mi'Cherev Nafshi mi'Yad Kelev Yechidasi" - mi'Cherev is the sword [of Amon used to kill] Uriyah, and mi'Kelev is from the dog of (through which was killed) the Chasid.

R. Yudah bar Pazi went up to the upper story of the Beis Midrash and saw two men having relations together. They said to him "Rebbi - put your mind [not to reveal the matter], for you are one and we are two." (You will not be believed about us, but we would be believed to testify falsely about you.)