"The post mortem report mentioned asphyxia, as a result of hanging, the cause of death which rules out the allegation of murder," Superintendent of Police D K Rai said.
He said other than that from hanging, there was no injury mark on the victim's body. There was a minor abrasion on her right leg.
"To confirm the second allegation of rape, a slide had been sent to women hospital for testing and a final conclusion will be drawn only after the report is received," the SP said.
The victim's mother in her complaint had alleged that the girl was raped and murdered.
He said the post mortem was conducted by a panel of three doctors and the procedure was video-recorded to avoid any doubt.
Missing since Friday evening, the girl, who was allegedly raped, was found hanging from a tree inside the premises of Nighasan Police Station. Eleven policemen posted there were suspended after her body was found.
Meanwhile, the NHRC has decided to send a probe team after it took suo motu cognisance of media reports alleging that a teenage girl was raped and killed in a police station in Lakhimpur.
"The Commission has decided to depute its investigation team for conducting an on-the-spot inquiry into the incident.
"It has also decided to issue notice to the Director General of Police of the state calling for a detailed report into the incident within four weeks," an NHRC spokesperson said in New Delhi.