Punjab Advocate General Rupinder Khosla's 75-year-old mother-in-law was found murdered in her house in Chandigarh on Thursday.
Police said Gurbal Maninder Mann was raped before being killed.
She was living alone in her house, and police said that she had been smothered to death.
Her body was found lying semi-nude in the bedroom, which was locked from inside, they added.
A forensic and post mortem report is awaited before confirming the rape.
Police said the crime may have been committed five days ago and appeared to be the handiwork of more then two men.
The incident came to light when Khosla landed at Mann's house to celebrate the birthday of his daughter, who had come from the US and was to return on January 8.