Cox asked a noted arson analyst, Gerald Hurst, to take a look at Willingham's case in light of advances in arson forensics. He produced a report that contradicted the original evidence in 1991 that labeled the house fire as arson.
The four-page report was given to Perry in the days leading up to Willingham's execution, but Perry, now a Republican presidential candidate, decided it didn't merit a stay, Time magazine reported Tuesday.
In a Sept. 7 Republican presidential debate, Perry defended the 234 executions that have taken place in Texas since he took office.
In Texas, he said, "if you come into our state and you kill one of our children, you kill a police officer, you're involved with another crime and you kill one of our citizens, you will face the ultimate justice in the state of Texas, and that is, you will be executed."