Fifteen-year-old Keeling's bruised and half-naked body was found on popular Anjuna beach in the north of the Indian resort state eight years ago.
Her death made headlines worldwide, drawing attention to the dark side of a tourist destination that has long been a hangout for Western hippies and later highlighting India's sluggish justice system.
Police initially dismissed the teenager's death as an accident but opened a murder probe after Keeling's mother, Fiona MacKeown, pushed for a second autopsy which proved she had been drugged and raped.
MacKeown also accused local authorities of trying to cover up the death to protect drug gangs operating in Goa, a former Portuguese colony.
Several weeks after the attack, local men Samson D'Souza and Placido Carvalho were arrested and charged with culpable homicide not amounting to murder, using force with intent to outrage a woman's modesty and of administering drugs with intent to harm.
The move angered the victim's family who had wanted the defendants tried for rape and murder, but officers from India's Central Bureau of Investigation (CBI) said they lacked sufficient evidence to indict them on stronger charges.
Police allege D'Souza and Carvalho plied Keeling with a cocktail of drink and illegal drugs, including cocaine, before sexually assaulting her and leaving her to die by dumping her unconscious in shallow water where she drowned.
The trial began at a children's court in Goa's state capital Panaji in 2010 but has been plagued by numerous delays, including infrequent hearings due to a backlog of cases and a public prosecutor withdrawing from proceedings.
Final arguments were heard at the end of last month with the prosecutor arguing that dozens of bruises on Keeling's body were evidence of a struggle. Defence lawyers however said the teenager died an accidental death.
Vikram Varma, a lawyer acting for MacKeown, told AFP the prosecution's case was dealt a blow when a key witness, Briton Michael Mannion, refused to testify, but he is hopeful that some justice can finally be achieved.
"It was important for the judge to hear Mannion's testimony to convict. So that was a setback," said Goa-based Varma.
"(But) I'm keeping my fingers crossed that after all this struggle we may get a verdict of guilty," he added.
MacKeown told a British tabloid last month that she feared the men would walk free.
"We were close to putting it to bed once and for all but my heart has been broken again because Mannion cannot testify," she told The Sun newspaper.
The family was on a six-month holiday to India when MacKeown and her other daughters went on an excursion to the southern state of Karnataka, leaving Keeling in the care of a Goan family.
MacKeown, who is due to be in Goa for Friday's verdict, came in for heavy criticism back home for leaving her daughter without parental supervision.
She was only able to bury her daughter's body more than two years after Keeling died, when it was finally returned to her by Indian authorities after a long bureaucratic wrangle.
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