Mr. Heaphy’s firm interviewed witnesses, examined video and still photographs, and reviewed half a million pages of documents. What emerged, he said, was a failure to prepare, a failure to inform the public about what to expect, and a failure to protect people.

The Charlottesville police had not been trained in handling civil unrest, and did not consult with other departments around the country that had relevant experience, the report said.

Many officers “had never even tried on the ballistic helmet or used the shield that they were given that day,” Mr. Heaphy said at a news conference. “We talked to a lot of police officers who really didn’t have a sense of what they were asked to do.”

The Police Department and the State Police did not coordinate efforts — state officials did not even give their tactical plan to the city police — and the two groups could not talk to each other on their radios. Unknown to the city police, Mr. Heaphy said, “the state police were told, ‘You are here to protect the park,’” and not to respond to violence.

Days before the rally, City Council members insisted that the site be changed from Emancipation Park to another location, over the Police Department’s objections. Though that plan was eventually dropped, it hindered preparations.

The night before the Aug. 12 rally, Unite the Right forces marched without a permit onto the University of Virginia campus, carrying lit torches. At the base of a statue of the university’s founder, Thomas Jefferson, they fought with a smaller group of opponents.

“University officials were aware of this event for hours before it began but took no action to enforce separation between groups,” the report said. The university refused repeated offers of aid from the city police, until after the event had descended into a melee.