The girl's mother, Fiona McKeown, has been fighting to uncover what happened to her daughter since her bruised, partially clothed body was found near the shore on a Goa beach more than eight years ago.
McKeown told CNN she was "totally devastated" by the verdict. "I just feel really let down by the system," she said to affiliate CNN News 18. "I just don't have any faith in it anymore."
Officers initially said the 15-year-old drowned on Anjuna beach after taking drugs, but her mother rejected that account. She launched a campaign for a second autopsy, and investigators eventually confirmed Scarlett was sexually assaulted before her death.
Local media and a state minister said at the time that police covered up the killing
to protect Goa's tourism industry.
Goa Chief Minister Laxmikant Parsekar expressed disappointment at Friday's verdict. "It has broken my heart as well," he said, saying he hoped there would be an appeal to a higher court.
"How can I appeal?" I can't appeal," Scarlett's mother said to CNN. "I'm just a tourist here. The CBI has to appeal."
McKeown's attorney, Vikram Verma, confirmed that only India's Central Bureau of Investigation
, or CBI, can appeal the decision.
"Even if the CBI takes it to the High Court, unless it goes through fast track, we'll probably be waiting for another eight years for a ruling," he added.
'It's been a long eight years'
Federal police said in 2008 that a suspect drugged the young girl with cocaine, alcohol and ecstasy pills, and then raped her before leaving her unconscious on the beach to drown. The case went to went to trial in 2010.
Verma, the lawyer, told CNN the trial had taken so long because all aspects of the case had to be examined. He also said the accused were out on bail during the trial
, prolonging the process.
"It's been a long eight years as I have been unsure of where I stood most of the time," McKeown told CNN News 18
before the verdict. "Those who killed my daughter perhaps had the confidence that I would not be able to last the slow process of a trial. But my resolve to stand up and fight for my daughter's justice has not diluted."
Her daughter's death became a local and international media sensation and even inspired a Bollywood film.
While waiting for India's notoriously slow legal system, McKeown has had to field a barrage of lurid accusations about drug use by her daughter and the teen's sex life
Her parenting was also questioned
since she was in a neighboring state when her daughter died. According to McKeown, Scarlett was left in the care of a trusted male friend and his aunts.