Death row convicts can't rely on an eleventh-hour appeal, although some like Richard Glossip secured a fourth stay of execution in 2015 when the legalities of execution came into question. Glossip, convicted in 1997, maintains his innocence, highlighting the possibility of states executing the wrongfully convicted. Controversial executions make up a large number of capital punishment cases in the United States, in part due to new forensic science capabilities. With capital punishment comes the burden to make sure guilt is proven beyond a reasonable doubt. US executions must be consistent with the Bill of Rights and established case law. Minors or those with diminished mental capacity can't be executed, and the punishment can't be cruel or unusual. This means the humane punishment - no torture or degradation - has to match the severity of the capital offense.
Unfortunately, these rules have been broken quite often in death penalty cases. Especially in the early 20th century, minority suspects were often given incompetent defenses with trials presided over by hostile judges and juries. Children have been executed, along with suspects whose mental capacity left them unfit to stand trial. And many people have met their ends proclaiming their innocence - only to be proven right decades later.
Here are some of the most controversial capital punishment cases in US history.