The state of Mississippi is preparing to execute an African-American prisoner tonight, despite an unusual admission from the FBI that its original analysis of the evidence contained errors. Willie Jerome Manning was convicted of murdering Jon Steckler and Tiffany Miller, two white college students, in 1992. The execution is going ahead after prosecutors and state courts refused to allow new DNA testing that could prove Manning’s innocence. The Justice Department sent a letter saying one analyst’s testimony at trial “exceeded the limits of the science and was, therefore, invalid.” Manning’s attorneys argue that no physical evidence ties him to the murders and that testing hair samples and other evidence could identify a different killer. But in a 5-to-4 decision last month, Mississippi’s state supreme court refused to grant a new DNA test, citing what it called “conclusive, overwhelming evidence of guilt.” On top of the denied DNA test, Manning’s attorneys say prosecutors relied on two key witnesses whose credibility has since come under question. Concerns have also been raised about alleged racial bias in the selection of the jury that found Manning guilty. “We need someone to step in,” says Vanessa Potkin, a senior staff attorney at The Innocence Project. “It is unconscionable that an execution would go forward where there is biological evidence that can cut to the truth and show whether or not he did the crime. What is anybody afraid of?”