R. Bohm, "Deathquest: An Introduction to the Theory and Practice of Capital Punishment in the United States," Anderson Publishing, 1999.
W. Ecenbarger, "Perfecting Death: When the state kills it must do so humanely. Is that possible?," The Philadelphia Inquirer Magazine, January 23, 1994.

injection as a means of execution, though it would be five more years until Charles Brooks would become the first person executed by lethal injection in Texas on December 7, 1982. Today, all of the states that have the death penalty use this method.
In 1924, the use of cyanide gas was introduced as Nevada sought a more humane way of executing its inmates. Gee Jon was the first person executed by lethal gas. The state tried to pump cyanide gas into Jon's cell while he slept. This proved impossible because the gas leaked from his cell, so the gas chamber was constructed.
Seeking a more humane method of execution than hanging, New York built the first electric chair in 1888 and executed William Kemmler in 1890. Soon, other states adopted this execution method. Today, electrocution is not used as the sole method of execution in any state.
although lethal injection is allowed as an alternative method. The most recent execution by this method was that of Ronnie Gardner. By his own choosing, Gardner was executed by firing squad in Utah on June 17, 2010.
execution used in the United States. Hanging is still used in Delaware and Washington, although both have lethal injection as an alternative method of execution. The last hanging to take place was January 25, 1996 in Delaware.
The Federal Death Penalty
Innocence The Supreme Court addressed the constitutionality of executing someone who claimed actual innocence in Herrera v. Collins (506 U.S. 390 (1993)). Although the Court left open the possibility that the Constitution bars the execution of someone who conclusively demonstrates that he or she is actually innocent, the Court noted that such cases would be very rare.