He was one of hundreds of thousands of victims of what has been called one of the worst mass atrocities of the 20th century: the state-sponsored purges of those suspected of being Communists and their sympathizers in Indonesia in 1965-66. Half a million people or more, many of whom had no connection to Communism, are estimated to have been killed, and hundreds of thousands of others were held in detention centers for years.

Survivors like Mr. Sukanta, now 76, have long demanded that the government give a full accounting of that dark period, to no avail. But some of them hope that a two-day symposium on the killings, starting Monday in Jakarta, will be a first step toward an official acknowledgment of what happened.

It will be the first time that a public discussion of the atrocities has been endorsed by the government, which for decades maintained that the bloodshed was justified to save Indonesia from a Communist takeover, while violently suppressing challenges to that official narrative.

The government is not organizing the symposium, but it has made its approval clear; Indonesia’s security minister, Luhut B. Pandjaitan, will deliver the opening remarks. Such official backing is rekindling hope among survivors and activists that a truth and reconciliation commission might be established to finally explain what happened half a century ago, and why.

“We hope this is the start to revealing everything that happened during those days,” said Atmadji Sumarkidjo, a special assistant to Mr. Luhut.