Since its introduction in 1977, lethal injection has been the most commonly used method of execution by states with the death penalty. While it’s often viewed as more humane than other methods, when the curtain is pulled back, it is tainted with error, ineptitude and secrecy that has led to many botched executions and unnecessary suffering. University of Richmond law professor and death penalty scholar Corinna Barrett Lain’s debut book “Secrets of the Killing State” explores the secretive world of lethal injection in Missouri and throughout the U.S.