Short version if you don't want to watch the video: Cameron Todd Willingham was executed for the death of his three daughters in a house fire. At the time, the forensics of arson were based on guesswork, and more recently, it's been discovered that a lot was what was thought to be evidence of arson is actually just normal traces of accidental fires.
The video includes Jack Johnson, the prosecutor (now a judge) who believes that Willingham was guilty, even though there was no solid evidence against him, and who smiles a lot when claiming that such things as being an Iron Maiden fan makes it plausible that he (Willingham) was a satanist.
Link thanks to The Agitator. Scurrilous speculation is entirely my own.