Central police commander Laimo Asi said the man reportedly followed her to the garden on the 6th of September and sexually attacked then killed her.
The man had been watching the girl the day before and had monitored her movements, leading to her attack.
PPC Asi says the girl was buried in a shallow grave near the riverside.
She was discovered by a group of youth on the 14th of September.
Police are now investigating the case, with the community asked to come forward with any information into the whereabouts of the suspect.