Mishpatim: Ruling With Clarity: Mitzvah 82 – Concept 543
“Do not be a follower of the majority for evil.” (Exodus 23:2) The court must not execute through a majority of one, but a majority of two is required. (Rambam, Hilchot Sanhedrin)
If the court ruled unanimously that someone is guilty and should be executed, he is sent free. The unanimous decision is an indication that he did not have good advocacy.
A majority of only one indicates that the matter is not clear. It is too close of a decision to allow someone to be executed. The court must convey both a sense of fairness and clarity when ruling in capital cases.