Updated

The Latest on Missouri's planned execution of inmate Marcellus Williams (all times local):

1:15 p.m.

St. Louis County's prosecutor says there is "zero possibility" that an inmate who is scheduled to die is innocent of the fatal stabbing that put him on death row.

Marcellus Williams is due to be executed at 6 p.m. Tuesday for fatally stabbing former St. Louis Post-Dispatch reporter Lisha Gayle during a 1998 robbery at her home in University City, a St. Louis suburb.

Williams' attorneys cite DNA evidence on the murder weapon that matches another unknown man, but not Williams. But St. Louis County prosecutor Bob McCulloch says the DNA tests were simply inconclusive.

McCulloch says there is ample other evidence that Williams committed the crime.

Williams would be the second man executed in Missouri this year.

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10:40 a.m.

Death penalty opponents are protesting Missouri's planned execution of an inmate who maintains his innocence.

Missourians for Alternatives to the Death Penalty and other groups are organizing rallies and vigils throughout the state ahead of the scheduled 6 p.m. Tuesday execution of Marcellus Williams.

One will take place outside of the Capitol office of Republican Gov. Eric Greitens, whom Williams has asked for clemency.

Williams was sentenced to death in the 1998 fatal stabbing of Lisha Gayle, a former St. Louis Post-Dispatch reporter who left journalism for social work. Authorities say she surprised Williams while he was robbing her home in the St. Louis suburb of University City.

Williams' attorneys contend that testing conducted in December using techniques that weren't available at the time of the killing showed that DNA found on the knife matches an unknown man, but not Williams.

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12:05 a.m.

Missouri is preparing for its second execution of 2017, even as condemned inmate Marcellus Williams continues to declare his innocence.

Williams is scheduled to die by lethal injection at 6 p.m. Tuesday at the state prison in Bonne Terre for the 1998 stabbing death of Lisha Gayle. The onetime St. Louis Post-Dispatch reporter surprised the burglar and was killed at her University City home.

Attorneys for Williams contend that testing conducted in December using techniques that were not available at the time of the killing showed DNA found on the knife matches an unknown man, but not Williams. They say previous DNA testing of hairs from Gayle's shirt and fingernails also excluded Williams, and that footprints at the scene did not match Williams.