A dashcam video of another 2014 fatal shooting of a black man by a Chicago police officer became public Monday, with Cook County's top prosecutor explaining in unusual detail her reasons for not charging the officer. Here are the key parts of the case:

THE ANNOUNCEMENT

Anita Alvarez, the county state's attorney, cited "the totality of the evidence" when announcing she would not charge Officer George Hernandez in the death of 25-year-old Ronald Johnson III, who Hernandez shot in the back as he fled from officers.

The shooting occurred just eight days before Officer Jason Van Dyke, who is white, shot 17-year-old Laquan McDonald, who was black, 16 times. Alvarez charged Van Dyke with first-degree murder last month, hours before the release of dashcam video of McDonald's death, which led to days of protests and the ouster of the city's police chief.

On Monday, Alvarez's news conference came about two hours after the U.S. Justice Department announced it would investigate the Chicago Police Department for patterns of racial disparity in the use of force in the aftermath of McDonald's shooting.

Johnson's family and its attorney rejected Alvarez's decision, calling it a "joke" and dismissing authorities' assertions that Johnson was armed. They have sued the city over the death.

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THE EVIDENCE

Alvarez said officers encountered Johnson after responding to reports of shots fired in a city neighborhood. She played 911 calls and radio traffic among officers as a way of explaining what Hernandez knew about the scene when he arrived: Shots had been fired and men with guns could be seen running into a building.

Alvarez said Hernandez would have been able to see a man struggle with a plainclothes officer before breaking away and fleeing on foot and could hear officers shouting for the man — Johnson — to stop and drop his weapon. He was running in the direction of other officers. Hernandez fired five times, Alvarez said, hitting Johnson twice.

Digital images of Johnson's hand show he was holding something, though it is unclear what, Alvarez said. She also added that DNA recovered from a gun found next to Johnson's body matched Johnson's DNA, and a matching bullet was found in a car where Johnson was sitting earlier that night.

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THE PRESENTATION

It's rare for Alvarez to go to such lengths to explain why charges were not warranted, but she has come under heavy criticism in recent weeks for waiting more than a year to charge Van Dyke.

Before showing the dashcam video in the Johnson case, she and Assistant State's Attorney Lynn McCarthy showed a long PowerPoint presentation that included radio communications and maps of the part of the city where the shooting happened. There were photographs of the gun she said was recovered near Johnson's body in a grassy area of a park, and digitally magnified images of Johnson's hand while he was running to show he was holding an object.

She also, unusually, showed a video of an unrelated shooting incident to illustrate her point that an officer could be in fear for his life from a man running away; it showed an assailant shooting an officer over his shoulder.

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THE REACTION

The attorney representing Johnson's family countered Alvarez's video presentation with one of his own later Monday — including parts of video and audio of a deposition that he took from Hernandez a month ago.

Attorney Michael Oppenheimer, who represents Johnson's mother, Dorothy Holmes, dismissed Alvarez's presentation as an "infomercial," said a witness was coerced into false testimony and said the investigation Alvarez relied on was incomplete and didn't include comments from key witnesses — including Hernandez himself.

The audio Oppenheimer presented of what he said was Hernandez's deposition had the officer saying that he wasn't concerned about charges being filed against him. Oppenheimer also suggested that police could have planted the gun found next to Johnson's body.

Phone and email messages seeking comment on Oppenheimer's claims were left for Alvarez's spokeswoman and were not immediately returned.