From Wikipedia :
" The law of evidence, also known as the rules of evidence, encompasses the rules and legal principles
that govern the proof of facts in a legal proceeding.
These rules determine what evidence must or must not be considered by the trier of fact in reaching its decision."
The Rules of Evidence vary from state to state, but generally follow Federal guidelines.
A signed affidavit is a legal statement, it does not meet "prima facia' evidence unless corroborated by another witness, written statement,
or a personal appearance by the witness in court.
Most evidence needs to be corroborated by another source, or witness, or it is considered 'hearsay', and that evidence,
while accepted by the court, is not given much weight or consideration in rendering a decision.
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