That Afternoon Began With Peaceful Demonstrations

The investigations also concluded 33 first responders and 21 officers sustained injuries during the four-day period.

The investigations were completed by Oakland Police Department's internal affairs division, the city's community police review agency, an independent contractor, and the police department's force review board. The groups overseeing the investigations reviewed more than 300 use of force complaints from protesters and they determined no significant injuries to community members occurred, Armstrong said.

"The City of Oakland faced four days of gatherings, most of which were peaceful, but we had protests that became violent, that became challenging for the department and the city," Armstrong said.

On May 29, officers deployed tear gas at protestors who they say were throwing bricks and vandalizing local property. The levels of force used by officers on this day were found to be mostly in compliance with department policy, Armstrong said. Six officers and seven civilians were injured in the protests, a statement from the department told CNN at the time.

Minimal force was used the following day on May 30.

Officers did use force on May 31, when a caravan of vehicles traveled into Oakland with the intention of looting businesses throughout the city, Armstrong said. Calling it "one of the most violent days," Armstrong said the armed protestors looted and vandalized a Walgreens, various other pharmacies, medical marijuana dispensaries, and several small businesses in the city's most marginalized communities, like the Fruitvale area.

He opened his door to protesters in need of shelter. They changed his life forever

The 33 instances of excessive force came from June 1, Armstrong said. A protest near the area of 8th Street and Broadway Street became violent as bottles were thrown at officers, he said. The police officers deployed tear gas in response. That afternoon began with peaceful demonstrations, but several dozen protesters were taken into custody after being on the streets past curfew, CNN reported.

The officers deployed tear gas after feeling limited by the lack of law enforcement personnel and resources, Armstrong said.

"In order to use that level of force, there must be imminent danger to the officer or community [and] during these investigative processes, they determined that did not exist," Armstrong said.

The department said there will be stricter requirements for officers to deploy tear gas in the future and it will no longer be carried into protests without command approval, Armstrong said. Rubber bullets are not part of the department's inventory and were not used during the incident, Armstrong added.

"It's my effort to ensure the community as they come to Oakland that they can peacefully assemble and if they march or protest in our city, they don't have to worry about deployments outside of policy," Armstrong said. "Clear accountability will happen to those that violate policy."

Officers who were reprimanded are permitted to appeal any disciplinary action taken against them, Armstrong said.