Story highlights Mark O'Mara: Marcellus Williams, convicted of murdering Felicia Gayle in 1998, has been granted a stay of execution

A lack of DNA evidence on the murder weapon suggests Williams may be innocent, writes O'Mara

Mark O'Mara is a CNN legal analyst and a criminal defense attorney. The opinions expressed in this commentary are solely those of the author.

(CNN) Marcellus Williams was convicted 16 years ago for the 1998 murder of Felicia Gayle, a former reporter in St. Louis, Missouri. She had been stabbed dozens of times and left to die with the murder weapon, a knife, still embedded in her.

A jury of 12 people looked at the evidence, listened to witnesses and decided beyond a reasonable doubt that Williams was guilty. The problem is that the system may have failed in several significant ways.

I don't know yet if he's guilty or innocent. There's simply not sufficient time to review it all and come to an opinion, but it's time to take time. Missouri Gov. Eric Greitens, who just hours before Williams' scheduled execution on Tuesday granted a stay and empaneled a "board of inquiry" to look into the case, should be congratulated on taking a common sense, "let's be certain" approach to a difficult issue.

Mark O'Mara

We also know two facts that should lead to an immediate stay of execution and a complete review of the case. Gayle was savagely stabbed to death with a knife that was left in her chest and Williams' DNA was simply not on that knife.

The prosecutors of the state of Missouri, in opposing a stay of Williams' execution, made a mistake. We should simply pause to make sure we do it right, particularly when there is compelling evidence that Williams may be factually innocent. We've known for decades that DNA evidence is very precise and, although not completely infallible, can by its existence damn a person or exonerate one.

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