My colleague David Nimmer points to this passage from the Talmud (I quote here from a 1903 edition). The first two statements -- that a Sanhedrin that executes one person in seven years, or seventy years, is considered cruel -- are pretty well known, and are often used to assert that Jewish law is hostile to the death penalty, in spite of the Old Testament's frequent endorsement of the penalty. The Simeon ben Gamaliel response, however, is not as well known:
The Sanhedrin who executes a person once in seven years, is considered pernicious [often translated "cruel"].
R. Eliezar b. Azariach said: Even one who does so once in seventy years is considered such.
Both R. Tarphon and R. Aqiba said: If we were among the Sanhedrin, a death sentence would never occur.
To which R. Simeon b. Gamaliel said: Such scholars would only increase bloodshed in Israel.
Whoever is right, the matter is still being equally hotly debated, by Jews and others, thousands of years later.