The body with cut marks bundled in a sack was found on July 1 in a deserted paddy field under Jagatpur police station area on the outskirts of the city after she went missing on June 29, police sources said.
Satyabrata Sahu (16), his friend Ramesh Kandi (16) and a gardener-cum-watchman Bisweswar Mahakud (30) were arrested, the sources said.
They were arrested under section 364 (kidnapping), 368 (keeping in confinement), 376 (rape), 302 (murder) and 34 (common intention) of IPC, they said.
Police said Satyabrata took the victim to a farmhouse where she was allegedly raped and killed on Saturday night by the three accused. The murder weapon was seized from the farmhouse, they said.