I wasn't really looking, but since I like history and to teach the ignorant:
HISTORICAL EVIDENCE OF DETERRENCE:
"There are many examples of how the death penalty deters murder, most haven't even been listed on this webpage. But here is an example of how the use of consistent executions have dramatically improved certain societies.
In the 1800s, in English occupied India, there was one of the worst gangs of murdering thieves the world has ever known, the Indian hoodlum band known as the Thuggees. Through the course of their existence, dating back to the 1550s, the Thuggees were credited with murdering more than 2,000,000 people, mostly wealthy travelers. The killer secret society plagued India for more than 350 years. The Thuggees traveled in gangs, sometimes disguised as poor beggars or religious mendicants. Sometimes they wore the garb of rich merchants to get closer to unsuspecting victims. One of their principles was never to spill blood, so they always strangled their victims. Each member was required to kill at least once a year in order to maintain membership in the cult. But they killed in the name of religion. The deaths were conceived of as human sacrifices to Kali, the bloodthirsty Hindustani goddess of destruction. It came to pass that the Thuggees began to kill using pickaxes and knives. According to legend, the Thuggees believed that Kali devoured the bodies of their victims. The story goes that once a member of the society hid behind a tree in order to spy on the goddess. The angry goddess punished the Thuggees by making them bury their victims from then on.
The ruling British government worked very hard to stop the Thuggee religion and its murderous practices. Between 1829 and 1848, the British managed to suppress the Thuggees by means of mass arrests and speedy executions. Indeed, rows and rows of Thuggees were left hanging from the gallows along the roads by the dozens. This not only established a zero recidivism rate, but it also greatly discouraged new membership into the cult. The most lethal practitioner of the cult of Thuggee was Buhram. At his trial it was established that he had murdered 931 people between 1790 and 1840. All had been strangled with his waistcloth. Burham was executed in 1840. Appropriately enough, he was hanged until he strangled. In 1832, the Agent to the Governor-General of India, F. C. Smith had this to say about the Thugees and their deeds.
I have never heard of such atrocities, or presided over such trials, such cold-blooded murders, such heart-rending scenes of distress and misery; such base ingratitude; such a total abandonment of the very principle which binds man to man; which softens the heart and elevates mankind above the brute creation...mercy to such wretches would be the extreme of cruelty to mankind...blood for blood.
In 1882, the British government deemed the problem solved with the hanging death of the last known Thuggee. "
P.S.: For extra credit: