This year, a sergeant in a front-line unit who had been bullied and ostracized was accused of going on a shooting rampage in June and killing five fellow soldiers. “You may have thrown a stone for fun, but for the frog hit by it, it is fatal,” the sergeant wrote in a note. He shot himself after an armed standoff with his unit, but survived.

In South Korea, a country that was ruled by generals or former generals until the 1990s, the military has never faced as much scrutiny as Parliament has applied to other parts of the government. Military leaders argued over the years that morale and effectiveness would suffer if the armed forces were exposed to too much criticism, openness and outside interference.

Critics say the military is losing the public’s trust by failing to deliver on its repeated promises to end the abuse problem. For many South Koreans, the fact that the military kept the severity of Private Yoon’s case largely to itself for almost four months was almost as shocking as the details of his ordeal.

One of the angry comments received by the Defense Ministry was from a man who said he was considering helping his son avoid military service with surgery to deliberately damage a knee or other body part and make him medically unfit, as some young men have been known to do. That would be far better, the commenter said, than “having him killed like a dog by human scum in the military.”

Details from the military investigation of Private Yoon’s case were made public by the Center for Military Human Rights in Korea; the group has not said how it obtained the report. The director of the center, Lim Tae-hoon, said the case showed “how an entrenched evil mechanism of violence is inherited, as the victim turns into an abuser.”

The enlisted men in Private Yoon’s unit, a medical team attached to the 28th Division stationed north of Seoul, formed their own strict hierarchy, with the senior sergeant ruling “like an emperor” over the junior soldiers, Mr. Lim said.

The sergeant, who has been identified only by his surname, Lee, treated his juniors, particularly the lowest-ranking private in the unit, like punching bags. After Private Yoon arrived in February, the other soldiers began doing to the newcomer what the sergeant and other superiors had done to them, according to the investigative documents.