John Thompson, a Louisiana man who spent 18 years in prison after the prosecutor in his case withheld exonerating evidence, has filed a complaint with the Justice Department seeking a federal investigation of that prosecutor, John Williams. The complaint alleges “a pervasive and unapologetic pattern of unethical improper conduct” perpetrated by Williams and his colleagues at the Orleans Parish District Attorney’s office.

Thompson served 18 years, most of them in the notoriously violent Angola Penitentiary after being found guilty of a murder he did not commit. He spent 14 of those years on death row until — weeks before one of his seven proposed execution dates — a team of pro bono lawyers discovered that prosecutors led by Williams had failed to disclose blood samples from the scene of the crime at Thompson’s original trial. Those samples showed that the perpetrator had type B blood. Thompson has type O blood. Eventually Thompson was granted a retrial and, in 2003, a jury took 30 minutes to find him not guilty.

Thompson went on to sue the Orleans Parish District Attorney’s office for failure to train its prosecutors and won a jury award of $14 million — one for each year he spent on death row — only to have that verdict overturned by a controversial 5–4 U.S. Supreme Court decision. While prosecutors conceded they had withheld evidence supporting Thompson’s likely innocence, the court held that the district attorney’s office could not be found civilly liable because the mistake by prosecutors did not stem from a deficiency in training.