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A Missouri man has been executed after killing two men as a teenager, despite several jurors in the case petitioning for a reduced sentence.

Michael Tisius, 42, died by lethal injection at a Missouri state prison on Tuesday evening local time.

Tisius was given the death sentence in 2010 for killing two sheriff's deputies in a failed bid to free a former cellmate.

He was the 12th man to be executed in the US this year.

Missouri's Republican governor Mike Parson rejected a clemency request for Tisius. A last-minute appeal for a stay of execution with the US Supreme Court was also unsuccessful.

According to prosecutors, the then 19-year old had turned up at the Randolph County jail in 2000 with Tracie Bulington, the girlfriend of his former cellmate Roy Vance.

Tisius then pulled out a gun and shot sheriff's deputies Jason Acton and Leon Egley, who were both unarmed.

However, he and Bulington were unable to find the keys to Vance's cell and fled. They were captured the next day after their car broke down.

Bulington and Vance were eventually sentenced to life in prison.

Lawyers for Tisius had argued that he should be spared the death penalty as he was 19 at the time of the killings and suffered from mental illness.

Six former jurors among the 12 who voted unanimously to recommend the death penalty also said in sworn affidavits that they now favoured life imprisonment instead of capital punishment.

However Governor Parson rejected the clemency request, stressing that Tisius had been provided with "due process and fair proceedings" for the "brutal murders".

In a final written statement, Tisius expressed "everlasting remorse" to the families of the men he had killed.

"I am sorry. And not because I am at the end. But because I truly am sorry."