A former US police officer was set to be executed Tuesday night for hiring a hitman to kill his wife some 30 years ago.

Unless he is granted a last-minute reprieve, Robert Fratta, 65, will receive a lethal injection in a Texas state prison.

Fratta has been in jail since 1994, when, according to prosecutors, he recruited an acquaintance who hired a contract killer to assassinate Farah Fratta, 33.

According to legal documents, the spouses were in the middle of a bitter divorce fighting over custody of their three children.

Robert Fratta "solicited many of his friends and acquaintances to kill her or to recommend someone who could kill her," court documents say.

"Initially, most of his friends thought that he was joking or blowing off steam, but as he continued to talk about it over time, some of them came to believe that he was serious."

Robert Fratta enlisted a man from his gym who then hired a hitman. According to US media, Fratta paid the hitman $1,000 for his wife's murder.

Fratta was first sentenced to death in 1996, but the verdict was overturned in 2007 over a technicality. He was resentenced to death in a second trial in 2009.

His lawyers have filed multiple appeals and have asked the US Supreme Court to halt Fratta's execution, alleging that testimony from a witness in the trial was obtained using hypnosis.

Robert Fratta and two other death row inmates in Texas have also sued the state prison system over its use of expired execution drugs, arguing that cruel punishment is prohibited by the US constitution.

Texas uses pentobarbital, a drug that is in short supply because pharmaceutical companies do not want to be associated with the death penalty.

If no reprieve is granted, Fratta will be the second death row inmate to be executed in the United States this year.