Ganguly also did not find convincing the police version that the four accused had tried to flee, and said the "right to trial of even the most heinous perpetrators of crimes cannot be snatched in this way".
"The incident is very unfortunate. I am unable to understand the police version of the incident.
"Police are claiming they took the culprits to the locality to do a reconstruction of the crime. Now the culprits are not terrorists. They were not armed. I agree they have committed the most heinous crime. If they had snatched the weapons of the police, then how did the police shoot them dead?" he asked.
Ganguly, who served as chief justice of Odisha and Madras High Courts, said when the police had taken to the spot the alleged perpetrators of such a heinous crime, they must have gone with a force.
"I don't find the police version of the four men trying to flee convincing. It is an indication of something sinister - that protectors of the law are taking the law in their own hand.
"However, heinous a crime somebody may commit, India's rule of law and constitution say he has the right to fair trial. The right of trial cannot be snatched in this way," said Ganguly, a former chairman of the West Bengal Human Rights Commission.
On Friday, more than a week after brutal gang rape and murder of a young veterinarian in Hyderabad, police shot dead all the four accused in an alleged 'encounter' near Shadnagar town of Telangana's Ranga Reddy district.
The accused were gunned down when they allegedly tried to snatch weapons from the police and escape. Police sources said they acted in self defence.
The incident occurred between 3 a.m. and 5 a.m. at Chatanpally near Shadnagar town, about 50 km from Hyderabad.
( With inputs from IANS )