The teenage girl, whose death led to major violence in parts of north Bengal, lost her life due to poisoning and there were no signs of any external injury, as per her postmortem report.
Alleging rape and murder of the girl, a mob went on a rampage in North Dinajpur district on Sunday, setting fire to several police vehicles and government buses on the National Highway 31 in Chopra area near Siliguri.
"No signs of external injury seen. Effects of poison. However, final opinion reserved pending till receipt of chemical examiners report," the post mortem report said.
The girl was allegedly abducted after she went out of her house at Sonapur village on Sunday morning to relieve herself.
She was found dead a few hours later, and the villagers alleged that she was raped before being murdered.
Police said they have so far arrested 16 people for their alleged involvement in the violence.
Members of the RSS-affiliated ABVP and Left-backed DYFI also protested in Jalpaiguri district's Dhupguri area over the incident, leading to tensions.