He remained on death row for 12 years, but it was only in the weeks leading up to his execution that convincing scientific evidence of his innocence began to emerge.

Of the 560 remaining files, they have re-examined 200, looking for cases with biological evidence and defendants who still claim innocence.

Go to the website of the New York-based Innocence Project to see the latest tally of exonerations that have taken place in America, after DNA evidence showed those convictions to be unsafe.