Makkot 7 - Capital Punishment was Infrequent, Laws of Inadvertent Killing
The phrase " By the word of two witnesses " additionally teaches that the judges must understand the language spoken by witnesses.
If two witnesses testify that a person was sentenced as a murderer by a certain court, and name the time, place, and witnesses in the case, that person is executed based on their words.
A sanhedrin that executes once in seven years is called a destroyer. Rabbi Eliezer ben Azaryah says, "Once is seventy years." Rabbi Tarfon and Rabbi Akiva say, "Had we been on the sanhedrin at the time when they still performed executions, no person would ever been executed." Rabban Shimon ben Gamliel says, "They would just increase the number of murderers in Israel," because they would have eliminated the criminals' fear of retribution.
One who kills a person inadvertently is exiled into a city of refuge. If one was lowering a cask from a roof with the rope and it fell on a bystander and killed him, the killer is exiled, but if he was raising a cask and the cask fell and killed, the killer is not exiled.
Art: Arnold Böcklin - The Isle of the Dead