Sanhedrin 33: Default Innocence

Returning to distinctions between monetary cases being tried and capital cases being tried -- what is the procedure for handling new evidence? The mishnah here is contradicted by a mishnah in Bekhorot -- where, here, in Sanhedrin, the case is retried, fundamentally, while in the other mishnah, the judge is responsible for the error. Why so? Also, reversing capital cases -- in the event of conviction, but not acquittal (that judgement stands). With exploration of various potential reversals, using various verses to illustrate the viability or impossibility of following through on a reversed decision to convict. Plus, the Sadducees and when the need to overturn a case was obvious even to to this sect.