The U.S. Supreme Court, the last body that could have halted the execution, declined to intervene in the case

A Missouri man has been executed, according to the man's legal team, even though the prosecutor's office that secured his murder conviction 21 years ago expressed doubts about the integrity of the case.

The US state executed the man despite him maintaining his innocence in the case and the prosecution's protest.

Williams was put to death despite questions his attorneys raised over jury selection at his trial and the handling of evidence in the case.

Marcellus Williams was sentenced to death in Missouri for the 1998 killing of Felicia Gay

Marcellus Williams had long proclaimed he was innocent in the 1998 fatal stabbing of Felicia Gayle in a St Louis, Missouri, suburb.

Attorneys for Marcellus Williams filed an appeal to the U.S. Supreme Court to stop his planned execution.

Marcellus Williams, who was convicted of a 1998 murder in suburban St. Louis, maintained he was innocent. But the courts and the governor were not persuaded.

The US state of Missouri has executed a man for the 1998 murder of a woman. The victim's family had pleaded with authorities to spare him and to turn his sentence into a life sentence.