Update: A few hours before Marcellus Williams was due to be executed Missouri Governor Eric Greitens issued a stay of execution.

On Tuesday night, the US state of Missouri is planning to execute Marcellus Williams despite a new report from a DNA expert that his lawyers argue supports his claim to innocence.

In 2001, Williams, who is now 48, was convicted of the 1998 killing of Lisha Gayle. But his lawyers say new DNA evidence could exonerate him. The Missouri Supreme Court, however, has refused to review that evidence.

Williams’ lawyer, Kent Gipson, has described the Supreme Court’s decision as “baffling”.

“We petitioned the court to look at the new evidence on August 14th, and less than 24 hours later they decided based on the court files that the execution should go ahead anyway. This is unprecedented,” Gipson told Al Jazeera.

Williams, who has always claimed he is innocent, was sentenced to death in 2001, three years after Gayle, a former newspaper reporter, was murdered in her home in a gated community in St Louis, Missouri. He was originally due to be executed on January 28, 2015, but Missouri’s high court decided to postpone the execution to allow time for new DNA tests to be conducted.

Those tests showed that the male DNA on the murder weapon, a knife, was not Williams’ but belonged to a third, unknown person.

“There is no physical evidence, no eyewitnesses that directly connect Williams to the murder, the DNA on the weapon wasn’t his, the bloody footprint at the murder scene wasn’t from Williams’ shoe and was a different size, and the hair fibres found weren’t his,” said Gipson. “It was someone else that killed Gayle, not Williams.”

How was Williams convicted?
During Williams’ trial, the prosecution based its case on the testimonies of two people, Henry Cole and Laura Asaro. Cole had shared a cell with Williams after he had been taken into custody on suspicion of being involved in Gayle’s murder. Cole said Williams had confessed to murdering the 42-year-old woman.

The other testimony was given by Laura Asaro, a convicted drug addict, who was Williams’ short-term girlfriend at the time of the murder. She claimed, among other things, to have seen scratches on Williams neck that were made by the victim.

“These scratches would leave DNA traces on the victim, but Williams’ DNA was not found underneath the victim’s fingernails, just like it was someone else’s DNA that was found on the murder weapon,” said Gipson.

“She also claimed she saw Williams with the victim’s driver’s licence, which is impossible because Gayle’s licence was left at the crime scene.”

Gipson believes both may have been motivated to give false statements in the hope of receiving a financial reward. “The victim’s family offered a reward of $10,000 for anyone with tips leading to the arrest of the person who murdered Lisha Gayle,” Gipson explained. “They both got paid by the victim’s family after their testimonies.”

With no forensic or eye witness testimony linking Williams to the murder, the prosecution based its case on these two witnesses. “At the time, we didn’t have the technology to do these DNA tests. But even now that there is indisputable scientific evidence exonerating Williams from the murder, the attorney general still thinks these testimonies hold more weight than the DNA evidence that shows Williams didn’t commit this crime,” Gipson said.