Mr. McDermott has suggested that the convicted soldiers were “victims of racial injustice.”

The case could be the largest Army court-martial of World War II. The largest court-martial of the war is thought to be that of 50 black sailors who were convicted of mutiny and sentenced to 15 years in prison for refusing to load ammunition aboard a ship at Port Chicago, a Navy depot 30 miles northeast of San Francisco.

The 28 soldiers in the Puget Sound case were stationed at Fort Lawton on Aug. 15, 1944, when Mr. Olivotto was found dead after a night of fighting among American and Italian soldiers on the base. Some American soldiers — white and black — objected to what they saw as lenient treatment of the scores of Italian prisoners held there.

The 28 black soldiers were among 43 initially charged with rioting, but charges were dropped against 2 of the 43 and the other 13 were acquitted.

Two defense lawyers, representing all 43 initially charged, had 13 days to prepare for trial. According to the board’s ruling, they did not have full access to a confidential Army inspector general’s report that Mr. Jaworski had seen, which suggested that evidence at the scene had been destroyed, and that white military policemen with animosity toward the Italians may have played a role in the riot.

“Under military law as it stands today, people would laugh,” said John Tait, an Army lawyer who reviewed the case for the board. “You don’t have two people represent 43 people. It just doesn’t happen. And when three people are charged with murder? No.”

The board’s decision instructs the Army to set aside Mr. Townsell’s conviction, and to change his dishonorable discharge to honorable, making his family eligible to receive back pay. Members of his family did not immediately respond to requests for comment on Friday.

The analysis used by the board in reaching its decision about Mr. Townsell would apply “to anybody who was convicted in that court-martial,” Mr. Tait said.