Prosecutors released dashcam video of the fatal Chicago police shooting of a black man a year ago just hours after the U.S. attorney general announced the Justice Department was investigating use of deadly force by Chicago police.

Ronald Johnson, 25, was fatally wounded by a Chicago officer as police responded to 911 calls reporting "heavy gunfire" in the area where he had just left a party, according to Cook County, Illinois, State's Attorney Anita Alvarez. No charges will be filed against the officer who shot Johnson.

Alvarez said Johnson was carrying a gun and refused to drop it when ordered by police. "He ignores all of those verbal commands and continues to run into the park." The officer who shot Johnson was chasing him, she said.

The video does not show "a physical struggle" between Johnson and another officer just before the shooting, the prosecutior said.

Johnson's family has been demanding for months that the police video be released and a federal court hearing was set for this week to ask a judge to order it.

The video release comes two weeks after the city made public dashcam video of the fatal police shooting of Laquan Johnson, 17. A Chicago police officer was charged with murder in that case.

Attorney General Loretta Lynch announced just hours before the Johnson death video was to be released that the Justice Department had opened a federal investigation of the Chicago Police Department's "use of deadly force" and alleged "pattern or practice in violation of the constitution or federal law."

.@theJusticeDept Opens Pattern or Practice Investigation into the Chicago Police Department→ https://t.co/sbDTe7pDWE pic.twitter.com/iQv3bcR3tN

-- Justice Department (@TheJusticeDept) December 7, 2015