Here are 10 developments in the story:
MM Kalburgi, a former vice chancellor of Hampi University, answered the doorbell at his home in Dharwad at around 8.40 am when he was shot in the forehead and chest.
The attackers had come on a bike, said Dharwad police chief Ravindra Prasad, and asked for "sir". They are yet to be caught or identified. A Special Investigation Team of the police will investigate the murder.
The family and friends of the 77-year-old, a well-known let ideologue and rationalist, say he had received many threats to his life, but he had never taken them seriously.
Because of the threats, Dr Kalburgi was given a gunman as an escort but the cover was withdrawn a year and a half ago. "My father didn't want to stop living for fear of death," said his daughter Ropadhiri.
The professor provoked the anger of some rightwing Hindu groups by speaking in support of writer UR Ananthamurthy, who had shared that as a child he had urinated on idols.
Dr Kalburgi's comment that the Lingayat community that he belonged to, is not Hindu, was also condemned by his critics.
A Sahitya Academy winner, Dr Kalburgi had several run-ins with rightwing groups who called his writings and speeches "anti-Hindu."
The police have filed a case against an activist of Hindu rightwing group Bajrang Dal, Bhuvith Shetty, for a threatening tweet after the killing.
Former Chief Minister BS Yeddyurappa, also a lingayat community leader, said: "Whatever be his views, he was a great historian and cannot be replaced. The culprits must be hanged."
In the last couple of years, there have been at least three such attacks. In August 2013, anti-superstition activist Narendra Dabholkar was shot dead in Pune while he was out for a morning walk. In February this year, social activist and veteran CPI leader Govind Pansare -- who was holding agitations against toll tax among other issues -- was shot dead in similar circumstances in Kolhapur.
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