If Gov. Jerry Brown (D) signs off, California could become the first state to ban the so-called “gay panic” defense.

A bill awaiting Brown’s approval would prohibit the use of the defense — the argument that a violent act was triggered by the revelation of a victim’s actual or perceived gender, gender identity, gender expression, or sexual orientation — in an attempt to downgrade a murder charge to manslaughter. It passed in the state Assembly last week by a 58 to 15 vote, and before that in the Senate with a vote of 25 to 9.

That the nation’s most populous state could soon ban the defense is a win for the National LGBT Bar Association, an association of legal professionals, students and affiliated groups that has been working to minimize the use of the defense for a decade, said Executive Director D’Arcy Kemnitz.

“But it’s going to be meaningful when we pass it in Wyoming where Matthew Shepard was murdered,” too, she said, noting that each state matters. The LGBT Bar Association and Equality California, an advocacy organization, both say the law would be the nation’s first.

At the urging of the LGBT Bar, the American Bar Association House of Delegates last August unanimously passed a resolution calling on federal, state, local and territorial governments to pass laws curbing the use and effectiveness of the “gay panic” and “trans panic” defenses.

“These defense strategies seek to excuse the crimes by saying that the victim’s sexual orientation caused their assailant’s violent reaction to them,” the ABA Journal noted at the time. “The ABA recommends that courts, when asked, instruct juries to ignore the victim’s gender or sexual orientation in its deliberations; it also recommends that laws might ban any use of such defenses in noncapital cases.”

The LGBT Bar has been fighting the defense for about a decade, sparked in part by the 2003 acquittal of a man accused of murdering Fulton County Assistant District Attorney Ahmed Dabarran, who was found bludgeoned to death in his home. Rodriguez Rashad Reed admitted to hitting Dabarran, claiming that the victim and two other men forced Reed to perform sexual acts and that the killing was committed in self-defense, according to contemporaneous reports. The gay panic defense was used in that case, Kemnitz says, and Reed was later acquitted.

The defense dates back to the 1920s when psychiatrist Edward Kempf coined the term “homosexual panic disorder” to describe patients who he said were gay, but refused to admit it, according to a legal review of the panic defense published last fall in the Southwestern Law Review by George Washington University Law professor Cynthia Lee. Gay panic was first listed in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders — which officially classifies disorders — in 1952, according to the LGBT Bar. It was rendered obsolete in 1973. Though Kempf never documented aggression among those identified as having the disorder, it morphed into a criminal defense in the 1960s and survives to this day.

The “panic defense” has been used to argue for lesser charges in various kinds of defenses, including mental defect defenses, such as temporary insanity, defense of provocation (the “heat of passion” defense) and self-defense. It was famously used — to no avail — in the trial over the murder of Matthew Shepard, the gay University of Wyoming student who was beaten to death and left tied to a fence in 1998. (One of Shepard’s assailants, Aaron McKinney, later acknowledged that his defense team fabricated the story underlying his “gay panic” defense.) The panic defense was also used in the trial over the killing of Gwen Araujo, who died in October 2002 after being beaten with a food can, frying pan and shovel by a group of men, two of them sexual partners. One tried to argue a “trans panic” defense, but failed, according to the LGBT Bar Association.

In her law review article, Lee argued that the defense is tied up in societal norms, “the product of a culture that privileges heterosexual male violence over other types of violence,” she wrote. Kemnitz agrees: “Every time a woman walks past a construction site and a bunch of guys make propositions to her, should she be able to respond in an assault in maybe even a murderous fashion?”

She says the organization plans to continue to push for the prohibition of the defense in other states. Attorney General Kamala D. Harris co-sponsored the bill, whose original sponsor was Assembly member Susan Bonilla.