An autopsy shows that Alicia Alli was strangled, which is in contrast to a note in one of her school books that amounted to a suicide threat.
Nothing was reportedly found around her neck at the time the body was found.
“The cause of death was given as asphyxia due to drowning, compounded by compression injury to the neck and blunt trauma to the head,” police said in a statement.
The body of Alicia Ali was found on the seawall at Turkeyen, ECD, on March 25, 2015.
Police spokesman Ivelaw Whittaker said during investigations into the circumstances surrounding her death, police on Thursday had discovered a suicide note in the room that had been occupied by Ali, which is believed to have been written by her and addressed to her mother.