NEW DELHI — A “clean chit,” in most of the English-speaking world, may bring to mind a blank piece of paper of inexplicable purpose. But in India it very clearly means the exoneration of a public figure by an investigating agency.

Probably the most famous “clean chit” was issued last year by a special investigation team to Narendra Modi, clearing the way for the opposition Bharatiya Janata Party to nominate him — days before the advent of an inauspicious period in the Hindu calendar — as its prime ministerial candidate for the general elections due this summer. The team, appointed by the Supreme Court, had investigated the allegations that Mr. Modi was complicit in the communal riots of 2002 in the western state of Gujarat, in which more than a thousand people were killed. He was then, as he is now, the state’s chief minister.

The manner in which the team and its chief, R.K. Raghavan, a retired police officer, conducted the investigation has been contentious. Now, a book by the journalist Manoj Mitta, “The Fiction of Fact-Finding,” accuses Mr. Raghavan of going to great lengths to shield Mr. Modi and of ignoring a wide spectrum of disturbing circumstantial evidence.

One of the intriguing revelations of the book is the approximate time when Mr. Modi, according to his own statement to the investigation team, learned of one of the worst massacres in his state. On the morning of Feb. 28, 2002, in Ahmedabad, Gujarat’s largest city, a Hindu mob began to gather around Gulbarg Society, an affluent, mostly Muslim neighborhood.