It took Mr. Modi almost a year after the first lynching, in September 2015, to clearly and firmly denounce the cow vigilantes. But the prime minister is a master at looking both ways when it comes to mob violence. Last month, after a landslide electoral victory in the northeastern state of Uttar Pradesh — where almost a quarter of India’s roughly 170 million Muslims live — he appointed a vicious priest, in full saffron robes, to be the state’s chief minister.

That man, Yogi Adityanath, has called for the family of the first lynching victim to be tried for illegally storing beef in their home. He has exhorted his followers to kill 10 Muslims for every Hindu killed. No sooner did he become chief minister than Mr. Adityanath led a crackdown against unlicensed butchers and abattoirs. Uttar Pradesh abounds in unlicensed businesses, but in singling out the meat industry — invariably run by Muslims — the politician-priest knew that he was in effect leading an attack on Muslim business with shades of Kristallnacht.

B.J.P. chief ministers across India are now falling over themselves in a quest to outdo one another in showing their love of the Indian cow, which, as Mr. Khan’s killing demonstrates, is animated partly by a hatred of Muslims. Last month, in Mr. Modi’s home state of Gujarat, cow slaughter was made punishable with life in jail; and in Chattisgarh, another B.J.P.-run state, the chief minister announced, “We will hang those who kill cows.”

Almost 60 percent of India now lives in B.J.P.-controlled states; there is no opposition left to speak of. What voices of moderation and reason there used to be within the B.J.P. are either too cowed to speak or feel that it is politically inexpedient to do so.

Vasundhara Raje, the chief minister of Rajasthan, is someone I grew up around in Delhi and have known all my life. She is aristocratic and is educated. She had many Muslim friends and even a Muslim boyfriend. She was a single mother, like mine. She smoked, she drank; she is well read and widely traveled. She certainly seemed the beneficiary of liberal values. That someone like her would now refuse to speak up for a poor Muslim farmer with small children who was lynched in her state is an indication of how poisoned the air has become in three short years since the B.J.P. came to power.

India is slipping beyond the pale. It is unfathomable that the ancient Hindu horror at the taking of life, any life — the very same doctrine of ahimsa, or nonviolence, that governed the beliefs of men like Mahatma Gandhi and the Rev. Dr. Martin Luther King Jr. — should in our time be used as a justification for murder. And not merely a murder in which one man is implicated, but rather a great televised spectacle in which a whole nation, through its silence, is complicit.