Missouri carried out the execution on Tuesday of a man whose capital conviction had been marred by controversies over insufficient evidence, compromised witness testimony, and racial discrimination.

In a statement, the Innocence Project, an advocacy group devoted to exonerating wrongfully convicted death row inmates, wrote of Williams’ passing:

Mr. Williams’ story echoes that of too many others caught in our country’s broken criminal legal system. A Black man convicted of killing a white woman, Mr. Williams maintained his innocence until the very end.

Williams was convicted in 2001 of the 1998 murder of journalist Felicia Gayle Picus in her home in a gated community in a suburb of St. Louis. When authorities arrived at the scene, they found ample physical evidence, including fingerprints, hair samples, bloody footprints, and the murder weapon. Still, police struggled to identify a suspect. The following year, the Picus family offered a $10,000 reward for information leading to the perpetrator’s arrest and conviction. At that point, two witnesses blamed Williams for the murder. This witness testimony proved instrumental, as none of the physical evidence at the scene could be tied to Williams.

Williams’ case has been challenged on multiple bases, including serious problems with the physical evidence — particularly in light of subsequent advances of DNA testing technology. Questions were also raised regarding the reliability of the witnesses who testified against Williams, and issues of racial discrimination.

These factors, particularly when viewed through the lens of the due process clause of the US Constitution, spurred many to call for clemency in Williams’ case. His advocates have even included local prosecutors. In January of this year, Prosecuting Attorney of the County of St. Louis Wesley Bell filed a motion to vacate Williams’ sentence, arguing that in addition to procedural and investigative issues, Williams’ trial had been marred by constitutional violations.

Among Williams’ most vocal advocates is the Innocence Project, an advocacy group that since 1992 has used DNA evidence to exonerate hundreds of wrongfully convicted death row inmates and advocate for criminal justice reform. The Innocence Project had said of the physical evidence: “There is no reliable evidence proving that Marcellus Williams committed the crime for which he is scheduled to be executed on Sep. 24. The State destroyed or corrupted the evidence that could conclusively prove his innocence and the available DNA and other forensic crime-scene evidence does not match him.”

Contributing to the controversy, Picus’ family publicly opposed Williams’ execution in light of evidence that DNA evidence related to the case was corrupted, according to the Innocence Project.

Despite these concerns, Missouri Governor Mike Parson announced the state would move forward with plans to execute Marcellus Williams at 6 pm local time on Tuesday. He said in a statement:

Capital punishment cases are some of the hardest issues we have to address in the Governor’s Office, but when it comes down to it, I follow the law and trust the integrity of our judicial system.

In dismissing calls for clemency, Parson cited Williams’ “robust criminal history” and the same witness testimony that featured in Bell’s motion to vacate and the Innocence Project’s advocacy materials.

Following Parson’s announcement, the US Supreme Court declined to intervene, removing the final barrier to Williams’ execution, which took place as scheduled. The Supreme Court justices voted along partisan lines, with the three justices appointed by Democratic presidents, Ketanji Brown Jackson, Elena Kagan, and Sonia Sotomayor, noting they would have opted to stay the execution.