Sanhedrin 2 - Monetary Cases are Judged by Courts of Three
Monetary cases cover most areas of civil dispute. Such cases are judged by courts of three qualified judges. Judges act on the basis of the testimony given by two qualified witnesses. There is no concept of a jury, and in general no concept of circumstantial evidence.
Cases of robbery and bodily injury are also monetary cases, adjudicated by courts of three qualified judges. Qualified in this context means that in addition to knowing the areas of relevant Torah law and relevant scientific discovery, they must also possess "semicha," an uninterrupted chain of ordination going back to Moses.
However, cases of loans can be adjudicated even by judges without semicha. This was an additional enactment made in order "not to close doors for the would-be borrowers," so that lenders would find it easy to resolve loan questions, and wouldn't always require ordained judges in cases of loan disputes.
Art: Anthony Van Dyck - Charles I in three positions