A new video has been released showing Chicago police shooting a suspect in the back

Assistant US Attorney Lynn McCarthy showed a dashcam video during a Monday press conference, showing a Chicago police officer shooting and killing Ronald Johnson in October 2014.

In the video, 25-year-old Johnson appears to be running away from police and toward a public park when Hernandez fires his gun at Johnson five times. Johnson is hit twice out of camera range. 

Hernandez will not have criminal charges filed against him because, as Cook County State's Attorney Anita Alvarez explained during the press conference, officers reported that Johnson had a gun and was running toward a police car containing two officers in the park. 

Alvarez focused on one still frame of the video, in which she said it appears Johnson is holding a gun, although Johnson's family's lawyer Michael Oppenheimer maintained that there is no gun visible in the video. 

Alvarez called Hernandez's actions "reasonable and permissible."

"Johnson could have easily turned around and quickly fired at the officers pursuing him or even fired as he ran," she  said. "Police officers are often forced to make split-second judgments in circumstances that are tense, uncertain and rapidly evolving about the amount of force that is necessary in any particular situation."

 Alvarez's decision was immediately panned by Oppenheimer, who in 2014 filed a federal wrongful death lawsuit on behalf of Johnson's family.

"This is a joke," Oppenheimer told reporters following the news conference. "It is the blind leading the blind."

Oppenheimer accused Chicago police of covering up Johnson's death by planting a 9-mm pistol on his body and later claiming Johnson had pointed it at them prior to the shooting.

"You can see no gun," he said. "There is no gun visible in Ronald Johnson's hand, because there was none."

Between 50 and 100 protesters from various activist movements - including Black Lives Matter, Action Now and Black Youth Project 100 - rallied on Chicago's South Side following the announcement. Another protest is scheduled for Wednesday morning, organizers said.

Earlier Monday, US Attorney General Loretta Lynch said the US Department of Justice would launch a wide-ranging investigation into the practices of the Chicago Police Department, focusing on the department's use of force and its accountability procedures.

The investigation comes after weeks of intense scrutiny surrounding the death of Laquan McDonald, a 17-year-old boy who was shot and killed by Chicago police eight days after Johnson's death.

Dashcam footage from the incident shows police shooting McDonald, who was black, 16 times as he walked away from police officers on a Chicago road, including multiple times after he had fallen to the ground.

The footage appears to contradict police reports that McDonald, who they say was holding a four-inch knife, had swung at them in an "aggressive, exaggerated manner."

Several top officials in the Chicago Police Department have resigned following the release of the video, including Chief of Detectives Dean Andrews on Monday. 

Chicago Mayor Rahm Emanuel fired police department superintendent Garry McCarthy on December 1, and Officer Jason Van Dyke was charged with murder, the first such charge against a Chicago police officer for an on-duty shooting in almost 35 years.