The United States has put to death more than 1,446 people since 1976, according to the Washington, DC-based Death Penalty Information Center (DPIC).

Texas leads the country in the number of executions carried out during that 41-year period, killing at least 540 people. Oklahoma and Virginia are tied for second with 112 executions each.

Meanwhile, public opinion on the death penalty seems to have been gradually changing. In September 2016, the Pew Research Center found that support for the death penalty was at its lowest in 41 years.

Since 1973, at least 157 people have been exonerated and released from death row. But the DPIC says that, as of July 2016, 2,905 people remain on death row.

The following are some of the cases where legal teams or campaigners are hoping to have death sentences overturned.

Duane Buck

In 1995, Duane Buck broke into the home of his ex-girlfriend, Debra Gardner, in Houston, Texas, after they broke up. Armed with two guns, he shot and killed Gardner and her friend Kenneth Butler while Gardner's three children were in the home. He was tried, convicted and sentenced to death in 1997.

Although Buck, now 53, never contested his guilt, the decision to deliver a capital punishment verdict rather than a life sentence has been thrown into question after a review of the racially charged testimony of an expert witness during the sentencing trial.

Psychologist Walter Quijano, who was introduced by Buck's own defence, testified that Buck would be dangerous in the future because he is African American.

READ MORE: Infographic - Breaking down the death penalty

In six other trials, Quijano testified to juries that black and Hispanic defendants were more likely to commit future crimes - the justification for sentencing them to death rather than life in prison.

In 2000, Texas Attorney General John Cornyn, who is now a US senator, reviewed those cases and admitted that Quijano's race-based testimony in those seven trials was "inappropriate".

Two years later, the other six death row inmates were granted new sentencing hearings, but Buck was not.

On February 22, 2017, the US Supreme Court ruled six-to-two in favour of granting Buck a chance at a new sentencing.

Jeffrey Wood

Jeffrey Wood, 43, was sentenced to death by a Texas court on March 3, 1996. His death sentence stems from the state's so-called Law of Parties.

During the early morning hours of January 2, 1996, then 22-year-old Wood and Daniel Reneau parked outside a Texaco petrol station in Kerrville, his hometown in central Texas.

While Wood waited outside, Reneau shot dead the station attendant and took off with an estimated $11,350 from the safe and cash register. Reneau was executed in 2002.

The Texas penal code defines a person as "criminally responsible for an offence committed by the conduct of another" if the individual acts "with intent to promote or assist the commission of the offence, he solicits, encourages, directs, aids or attempts to aid the other person to commit the offence".

READ MORE: Does a Texas man who killed no one deserve death row?

According to the DPIC, at least 10 people have been killed for their role as accomplices in murders since 1979. Five of those were in Texas.

Relatives and defenders of Wood, who reportedly has an IQ of 80, say he suffers from intellectual disability and emotional impairment.

On August 19, 2016, the Court of Criminal Appeals in Texas granted Wood a stay of execution and decided a state district court should re-examine the validity of testimony provided by Dr James Grigson, a forensic psychiatrist who testified that Wood was likely to be violent in the future despite never having examined him.

Grigson, who died in 2004, was expelled from the American Psychiatric Association and the Texas Society of Psychiatric Physicians for providing testimony against people he had never examined.

He was known as "Dr Death" for testifying against people facing the death penalty.

Terry Williams

When he was 17 years old, Williams killed 50-year-old Herbert Hamilton in Philadelphia, Pennsylvania. It was January 1984, and he reportedly lured Hamilton, who had allegedly repeatedly sexually abused the teen, and stabbed and beat him with a baseball bat until he died.

Six months later, Williams, then 18, and his friend Marc Draper lured Amos Norwood to a cemetery, where they beat him to death with a tyre iron. They later stole his car and took off to Atlantic City, New Jersey.

After surrendering himself to the police in July 1984, Williams was eventually convicted of third-degree murder in the death of Hamilton and was sentenced to 27 years. For Norwood's death, however, he was convicted of first-degree murder and sentenced to death.

Williams, however, had been repeatedly raped as a child, and Norwood and Williams were allegedly among the perpetrators. Several others accused Norwood of sexually abusing them while they were young boys.

Many of those involved in his original trial have publicly changed their minds since Williams was sentenced to death. Five jurors signed statements saying they wouldn't have voted for capital punishment if they had known of the evidence of sexual abuse.

READ MORE: Surviving death row

In 2012, Norwood's wife Mamie signed a declaration that she did not want Williams to be executed for her late husband's murder.

A lower court in Pennsylvania found that the Philadelphia District Attorney's Office had suppressed evidence that Norwood had sexually abused Williams.

In the 1980s, however, Ronald Castille was district attorney and personally approved the decision to pursue capital punishment against Williams.

Castille later became Pennsylvania Supreme Court Justice and refused to recuse himself from consideration of the inmate's death penalty - despite the lower court's finding that the district attorney's office had suppressed evidence under Castille.

On June 9, 2016, the US Supreme Court ruled in a five-to-three vote that Williams' constitutional rights had been violated.

Willie Jerome Manning

Willie Jerome Manning, 48, was convicted at two separate trials of two unrelated murders that took place in 1992 and 1993. He received two death penalty sentences. On death row for more than two decades, he has always maintained his innocence.

Manning was found guilty of the December 1992 killing of students Jon Steckler, 19, and Tiffany Miller, 22, in Starkville, Mississippi. He was later sentenced to death.

Five weeks after the killing of Steckler and Miller, 90-year-old Emmoline Jimmerson and her 60-year-old daughter, Albertha Jordan, were murdered during an attempted robbery. They were both beaten with an iron before their throats were slashed. A court also convicted Manning of their murders and eventually dealt him a second death sentence.

In 2011, a key witness recanted his testimony that he had witnessed Manning entering Jimmerson's apartment and filed affidavits that his testimony was false and the result of coercion.

In 2013, Manning was given an execution date for the Steckler-Miller case. He came within hours of dying before the court granted him a stay of execution.

In 2015, the Mississippi Supreme Court granted Manning a new trial for the Jimmerson-Jordan murders. He was exonerated and the charges were dropped.

Still on death row for the Steckler-Miller case, Manning has attempted to challenge hair and DNA evidence presented in his first trial.

The Federal Bureau of Investigation (FBI) has admitted that its forensic expert had made mistakes in testimony during the Steckler-Miller trial, and the US Department of Justice has told the prosecutor that "testimony containing erroneous statements regarding microscopic hair comparison analysis was used" against Manning.

If the forensic evidence eventually comes back in Manning's favour, he will be the first person to be exonerated for two separate death sentences.

Kerry Lyn Dalton

In March 1995, Kerry Lyn Dalton was sentenced to death for the murder of Irene Louise May in a trailer park in Live Oak Springs, California, more than seven years earlier. She was 28 years old and reportedly struggling with drug addiction at the time she was said to have killed May.

May's body, however, has never been located, and Dalton was primarily convicted based on confessions the prosecution alleges she gave to other people.

Victoria Ann Thorpe, Dalton's sister, wrote a book about the trial and has campaigned for Dalton's exoneration on the grounds that she was convicted on hearsay and there was neither a body nor a crime scene.

Dalton has yet to have an appeal heard, although her sister says it is prepared and they have been waiting for years.

Women make up less than two percent of the total death row population, according to DPIC.