Yunus had died on August 18 and his body was sent for postmortem examination as victim's uncle had alleged foul play in his death.
Lucknow: The forensic science laboratory (FSL) report of Yunus, a witness in the Unnao rape case who died recently, has ruled out poisoning as the cause of his death, a senior police official said Sunday
"The FSL report of Yunus has been received by SP Unnao. No poison has been detected in the viscera that were sent for chemical analysis," Additional Director General of Police (Law and Order) Anand Kumar said in Lucknow.
"This should end all speculation and settle the cause of his death beyond doubt", he added.
Yunus had died on August 18 and his body was exhumed on August 25 and sent for postmortem examination as the victim's uncle had alleged foul play in his death.
On Twitter, Congress president Rahul Gandhi had also termed the death "mysterious" and his burial "hurried".
The man's family, however, had said he died due to a liver ailment for which he was being treated since 2013.
Yunus was a witness in the CBI case registered after the death of the father of a minor who was allegedly raped by BJP MLA Kuldeep Singh Sengar. The rape victim's father died in April after being beaten up, allegedly by Sengar's brother and others.