To be sure, India’s politics are still vicious and violent, its society riven by religious, cultural and caste divisions that feed continuing discrimination and sporadically erupt in fury. Assassinations are frequent, corruption endemic and the courts largely feckless. Gujarat’s Muslims have never entirely recovered from the riots, and the state’s population is more religiously segregated than ever. No one can promise that large-scale riots will never return, but there are signs of hope.

The riots began on Feb. 27, 2002, when a train filled with Hindu pilgrims who had just visited a disputed shrine rolled into Godhra, a small city in eastern Gujarat, and was attacked by a Muslim mob. A fire started, and at least 58 Hindu pilgrims burned to death. Their charred bodies were brought to Ahmedabad, Gujarat’s largest city, and laid out in public, an act that all but guaranteed more violence. Huge mobs gathered to view the bodies.

At the time of the riots, Gujarat’s chief minister was Mr. Modi, a newly appointed functionary from the Bharatiya Janata Party, which advocates Hindu supremacy but faced sinking popularity in the state. Mr. Modi and his party endorsed a widespread strike.

Massacres began immediately. About 20,000 Muslim homes and businesses and 360 places of worship were burned. Later that year, Mr. Modi’s party was overwhelmingly re-elected. Mayors in the United States are thrown out when too much snow clogs streets; Mr. Modi let his streets be choked with blood and won election overwhelmingly.

Mr. Modi was following a familiar script. In 1984, Sikh bodyguards assassinated Prime Minister Indira Gandhi, and Hindu mobs in Delhi killed thousands of Sikhs in retaliation. The Congress Party, whose members encouraged the rioting, was rewarded later that year with a huge majority in Parliament. Commissions were formed to investigate, but there were few arrests and fewer convictions. After the 1992 Hindu-Muslim riots in Mumbai, in which 900 people were killed, commission recommendations were again ignored.

Commissions were impaneled after the Gujarat riots as well. A top state official told one panel that Mr. Modi ordered officials to take no action against rioters. That official was murdered. Thousands of cases against rioters were dismissed by the police for lack of evidence despite eyewitness accounts.