[Avodah] rules of evidence in halcha

[Dov Weinstock]

Background - The recent plot to bomb synagogues in Riverdale NY has taken a
new twist, with reports that the suspects were hapless recruits of an FBI
informant and that the whole thing smells of entrapment - i.e. there would
have been no attempt to engage in criminal activity without the FBI egging
them on.

Which made me curious about a couple of things.
1. Is there a similar concept in halacha, or do we find both parties liable
- i.e. the entrapper and the entrapped?
2. Is there anything similar to 'inadmissible evidence' - i.e., valid
evidence that the court will ignore because of the way it was obtained?

Dov Weinstock