SAN FRANCISCO - When Ohio’s Supreme Court last October backed the death penalty for Ashford Thompson, the ruling was close. Three of the seven justices felt that Thompson, convicted of killing a cop during a traffic stop, should have received life without parole. One called the shooting a tragic misunderstanding.

Two of the four judges who voted to uphold the death penalty were also in the middle of an election campaign to keep their seats. The same month the ruling was published, television ads lauded one of them, Justice Judith French, for one of her previous votes in favor of death.

Ohio is one of the states where high court judges are directly elected – and that, a Reuters analysis found, makes a big difference in death penalty appeals.

A review of 2,102 state supreme court rulings on death penalty appeals from the 37 states that heard such cases over the past 15 years found a strong correlation between the results in those cases and the way each state chooses its justices. In the 15 states where high court judges are directly elected, justices rejected the death sentence in 11 percent of appeals, less than half the 26 percent reversal rate in the seven states where justices are appointed.

Justices who are initially appointed but then must appear on the ballot in “retention” elections fell in the middle, reversing 15 percent of death penalty decisions in those 15 states, according to opinions retrieved from online legal research service Westlaw, a unit of Thomson Reuters.

Some academic studies over the past 20 years have mirrored the Reuters analysis, showing a relationship between the result in death penalty appeals and how state supreme courts are selected. The U.S. Supreme Court has not addressed these findings in its rulings.

Now, however, at least three current justices are sympathetic to the idea that political pressure on judges is a factor that leads to arbitrary, and perhaps unconstitutional, application of the death penalty.

The findings, several legal experts said, support the argument that the death penalty is arbitrary and unconstitutional because politics – in addition to the facts – influence the outcome of an appeal.

Courts have a responsibility to protect a defendant’s constitutional rights without political pressure, especially when the person’s life is at stake, said Stephen Bright, a Yale Law School lecturer who has worked on hundreds of death defenses. “It’s the difference between the rule of law and the rule of the mob,” Bright said.

In an interview, French said she and her colleagues cast their votes months before the Thompson opinion was published.

Justice Sharon Kennedy, the other Ohio Supreme Court judge running for re-election last year, said facing voters helps ensure that judges apply the law regardless of personal views on the death penalty.

“If you’re not answerable to the people, you have a wider slide to become what I would call an activist,” she said.

State supreme courts automatically review every death penalty verdict. Apart from examining whether any legal errors were made, judges must also weigh different factors to decide whether the death sentence is an appropriate punishment. Was it the defendant’s first offense or do they have a history of violent behavior? When a death sentence is reversed, the offender usually gets life in prison instead.

But as the Reuters analysis suggests, external factors may come into play. The election effect was a far stronger variable in determining outcomes of death penalty cases than state politics and even race.

Justices in states that supported Democratic President Barack Obama in the 2012 election reversed death sentences at roughly the same rate as those that went for Republican candidate Mitt Romney, at around 14 percent.

African-American defendants had lower reversal rates in both elected and appointed states. Nationally, death sentences were reversed 15 percent of the time for whites, compared with 12 percent for African-Americans, according to the Reuters findings.

Video: The verdict on the death penalty and elected judges

Reuters did not analyze the possible impact of the race of the victim on death penalty appeals. The analysis also excluded a category of death penalty appeals known as habeas challenges, because state supreme courts are not required to hear them and overwhelmingly refuse to do so.

Thompson’s attorneys are asking the U.S. Supreme Court to take up the case and throw out the Ohio ruling, arguing that prosecutors improperly dismissed a potential African-American juror. They also argue that it was “basically impossible” for French to vote against capital punishment while she was being praised during her election campaign for supporting death sentences.

Ohio prosecutors say Thompson only complained about political influence after he lost.

The Supreme Court is scheduled to review Thompson’s appeal at the end of September. His arguments could meet a difficult audience.

A SKEPTICAL COURT

The U.S. Supreme Court suspended the death penalty in 1972, finding that the punishment was often applied arbitrarily. After several states rewrote their laws to codify specific guidelines that could lead to death, like a violent criminal history, the Supreme Court in 1976 found those approaches constitutional.

Since then, majorities on the high court have taken a skeptical view of data used to argue that the death penalty is applied arbitrarily. In 1987, for instance, the court voted 5-4 that an academic study that showed a “racially disproportionate impact” of capital punishment in Georgia wasn’t enough to overturn a death sentence there.

In 2013, however, Justice Sonia Sotomayor cited a study showing that Alabama judges are more likely to impose the death penalty in election years, part of a failed effort to persuade her colleagues to review an Alabama capital case.

Last June, in Glossip vs. Gross, the high court voted 5-4 that the method of execution in Oklahoma is constitutional. In dissent, Justices Stephen Breyer and Ruth Bader Ginsburg cited studies showing capital punishment is arbitrary because of racial bias, as well as political pressure, “including pressures on judges who must stand for election."

Retired U.S. Supreme Court Justice John Paul Stevens, who has said he believes the death penalty to be unconstitutional, said in an interview that the Reuters findings “definitely lend support” to his side of the debate because they show how arbitrary capital punishment can be.