Nikki Kuhnhausen, 17, who was tragically killed after her assailant discovered she was transgender (Facebook)

Washington has just become the tenth US state to ban the ‘gay panic’ murder defence, passing the measure in honour of Nikki Kuhnhausen, a transgender teen who was killed last year.

The controversial ‘gay panic defence’ justifies violence against LGBT+ people by claiming that discovering a victim’s sexuality or gender identity caused the defendant to suffer from a state of temporary insanity.

It is a valid legal defence in the vast majority of the US, with the exception of California, Connecticut, Hawaii, Illinois, Maine, Nevada, New Jersey New York and Rhode Island.

On Wednesday, Washington followed suit as lawmakers passed House Bill 1687, also known as the Nikki Kuhnhausen Act.

The legislation is named for a 17-year-old girl who is believed to have been strangled to death with her own hair extension after her assailant learned she was transgender.

Kuhnhausen’s remains were discovered in December and a Vancouver man, David Y Bogdanov, has been charged with her murder. He has pleaded not guilty, but will now be unable to use the ‘gay panic’ defence in his trial.

The Nikki Kuhnhausen Act blocks a defendant from using any defence that is based on discovery or disclosure of the victim’s actual or perceived gender identity or sexual orientation.

It also prevents a claim of “diminished capacity” because the defendant did not fully comprehend the nature and gravity of the alleged crime.

The legislation passed the House earlier this month on a 90-5 vote and has now gone to governor Jay Inslee for his signature.

Clark County Democrat Annette Cleveland praised the bill’s passing after Kuhnhausen’s “violent and abominable killing”.

“By all accounts, Nikki would be alive today if not for a homophobia-based assault on her life,” Cleveland said in a statement. “And, I suspect, so would others who have been similarly victimised.”

She continued: “The terrible truth is that vicious assaults have been perpetrated against transgender people, as well as others in the LGBTQ community, for far too long. This bill is a start. It is long overdue, and we must still do more.”