Sanhedrin 27: Those Who Witness Falsely, Those Who Transgress - Can They be Trusted?

Some points on today's daf:

• Emim Zomemin, those who witness falsely, are disqualified retroactively
• The rabbis argue about at what time a false witness is disqualified
• Abaye is said to define the halacha: the false witness words are invalid from the time he testified
• a mumar, transgressor, who eats an animal that is treifa because it is destined to die within 12 months is also disqualified
• The rabbis argue about why he is disqualified and from what specifically he is disqualified
• They also argue about whether his crime was against the community or against G-d alone
• The rabbis discuss who is qualified to judge a capital case
• The story is told of a one who is sent to find out whether or not someone murdered someone else.  He found witnesses attesting to the killing.  He also found witnesses attesting to the transgressions of the first witnesses
• The rabbis note that a woman cannot testify just as the other four categories cannot testify and in spite of the fact that a false witness can testify

A new Mishna teaches that a brother, paternal/maternal uncle, sister's husband, paternal/maternal aunt, stepfather, father-in-law, and a gis, husband of a wife's sister cannot testify.  Neither can any of their sons, their sons-in-law, or a step-son (but his sons or sons-in-law are eligible).  

The first version of this Mishna only invalidated the testimony of an uncle, cousin, or any potential inheritor or anyone related at the time.  One who was previously related but was unrelated when seeing the testimony is permitted.  Once children are born, in-laws are related to their sons-in-law.  Close friends, those who bring gifts to a groom, and enemies, those who do not speak to their former friend for 3 days due to hatred are also disqualified.  The Sages say that Jews are not suspected of false testimony due to love nor hatred.

The rabbis discuss the potential sources of this statement.  There are competing proof texts suggesting that sons will only die for the sins of their fathers when they continue those sins (or when they could have stopped but did not), and that one will be punished for his brother's sins.  In this last case we are all responsible for each other.