The minister said the forensic reports received from Delhi's All India Institute of Medical Sciences (AIIMS) and Mumbai's J J Hospital and KEM Hospital said that the girls were not subjected to any sexual assault before being killed.
The reports said the girls died due to drowning, Patil said and added that advanced forensic tests are still being conducted to confirm if the sisters were sexually assaulted before being killed.
The three girls - aged five, nine and 11 - went missing Feb 14 from Lakhani village of Bhandara district, 65 km from Nagpur. Their mother lodged a complaint with the local police station after they did not return from school.
Patil said that the government is ready to transfer the case to the Central Bureau of Investigation (CBI) for further probe if the victim's family asks for it.