Why has Brenda Andrew been on death row for two decades? It has everything to do with sex.

In the United States, we no longer execute women for adultery. Or do we?

While the law says we cannot, the case of Brenda Andrew in Oklahoma makes clear that women’s consensual, extramarital sex is still seen as evidence of extreme depravity that merits harsh condemnation — up to and including the death penalty.

There has always been a double standard in this country when it comes to adultery. In colonial times, when adultery was a crime punishable by fines, stocks, whippings or death, there are few records of any prosecutions of married men. By contrast, the colonies frequently prosecuted married women for adultery. It remains a crime in Oklahoma. Although rare, adultery prosecutions throughout history have overwhelmingly targeted women and girls.

Brenda Andrew was sentenced to death in Oklahoma County in 2004 for the murder of her husband, Rob Andrew, from whom she was estranged. Although she is not the only woman to be convicted of murder in Oklahoma, she remains the only woman facing execution in the state. Her crime was not so unique that it would explain her sentence: Less than a year ago, Kristie Evans was sentenced to life imprisonment for conspiring to kill her husband. So why has Andrew been on death row for two decades?

The answer has everything to do with sex.

Throughout Andrew’s trial, Oklahoma County prosecutors Fern Smith and Gayland Geiger lingered on details of Andrew’s choice of clothing, hairstyles and cleavage. Witness testimony referred to her as a “hoochie.” Her dresses were too tight, her skirts too short, her shirts too low-cut. Smith and Geiger portrayed her as a harlot who could not control her sexual appetites. Urging the jury to convict her, Geiger displayed pieces of Andrew’s lingerie in shades of pink, red and black, and told the jury that it was not the kind of underwear a grieving widow would wear. The Oklahoman reported at the time that the display drew gasps from the courtroom.

But the prosecution didn’t stop there. They told the jury that in addition to being a seductress, Andrew was a bad mother. Why? Because she had sex with men other than her husband. And that, apparently, was reason to sentence her to die.

Research has shown that women’s sentences are often linked to their perceived transgression from gender roles. And the obedient, chaste wife is an archetype of femininity that has persisted throughout the centuries. Adultery may not be punishable by death, but sociologist David Baker found that in 42 cases of women sentenced to death for spousal murder from 1632 to 2014, the woman’s “adulterous” behavior was a major component of the evidence against her, even where it bore no relation to the crime.

We cannot state with certainty that the jury sentenced Andrew to die because she committed adultery. But we do know that Andrew had no history of violence and was known for acts of kindness and generosity in her community. And history tells us that women are judged harshly for infidelity, and that implicit bias often affects jurors’ decisions.

We agree with former Oklahoma Judge Arlene Johnson, who, after reviewing Andrew’s case, stated that the prosecution’s evidence “had no purpose other than to hammer home that Brenda Andrew is a bad wife, a bad mother, and a bad woman.” That’s why we are urging the entire Tenth Circuit Court of Appeals — which is poised to consider Andrew’s last appeal — to overturn her death sentence.

Sandra Babcock is a clinical professor at Cornell Law School and the co-founder of the Center on Gender and Extreme Sentencing. Valena Beety is a professor at Indiana University Maurer School of Law and the author of "Manifesting Justice: Wrongly Convicted Women Reclaim Their Rights." Susan Sharp is professor emerita of sociology at the University of Oklahoma who has written about women on death row.

This article originally appeared on Oklahoman: Guests: Is Brenda Andrew on death row for adultery?