Cyntoia Brown, a Tennessee woman sentenced to life for killing a man who picked her up for sex when she was 16, has been released from prison after serving 15 years.

Ms Brown’s release comes after former Tennessee governor Bill Haslam took the unusual step earlier this year of granting her clemency, calling the situation a “tragic and complex case”. Her release is a major victory for supporters who have maintained for years that the 2004 killing was self-defence.

Ms Brown said that she wants to help other women and girls suffering sexual abuse and exploitation. “I thank Governor and First Lady Haslam for their vote of confidence in me and with the Lord’s help I will make them as well as the rest of my supporters proud,” she wrote in a statement.

Her case stems from the killing of 43-year-old real estate agent Johnny Allen, with whom Ms Brown went home with after he approached her at a fast food restaurant in Nashville. Ms Brown would later tell police after the killing that she had pulled a pistol out of her purse, and shot Allen, because she thought he was grabbing a gun himself.

Prosecutors proceeded with first-degree murder charges for the killing, and added aggravated robbery because she had taken Allen’s guns and money, and fled in his pickup truck after killing him.

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In the years that followed her conviction in 2004, the US Supreme Court would rule that mandatory life sentences for juveniles was unconstitutional, but Ms Brown was nevertheless kept in prison after Tennessee prosecutors successfully argued that she was technically eligible for parole in 2055.

“Cyntoia Brown committed, by her own admission, a horrific crime at the age of 16,” Mr Haslam said in a statement announcing her clemency. “Yet, imposing a life sentence on a juvenile that would require her to serve at least 51 years before even being eligible for parole consideration is too harsh, especially in light of the extraordinary steps Ms Brown has taken to rebuild her life.”

Ms Brown met with prison counsellors to design a plan for her release, which will include time in a transition centre, according to a statement from the state’s department of corrections.

The case drew high-profile support from the likes of celebrities like Rihanna and Kim Kardashian, and came to be viewed in a different light with the rise of the #MeToo movement that drew attention to abuses of power.

Ms Brown said during her appeals process that she was a teenage runaway who had been caught up in an abusive relationship with a drug dealer who went by the name “Cut Throat” and forced her into prostitution.

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Ms Brown’s lawyers said that she was a victim of sex trafficking who not only feared for her life but also lacked the mental capacity to be culpable in the slaying because she was impaired by her mother’s alcohol use while she was in the womb.

“Did we somehow change the definition of #Justice along the way?” Rihanna wrote in Instagram in 2017, receiving 2 million likes. In addition to Rihanna and Kardashian, LeBron James, Meek Mill, and Amy Schumer had all advocated for her release.

Following the news of Ms Brown’s clemency, state senator Brenda Gilmore praised the decision.