By Mary Wisniewski and Justin Madden

CHICAGO (Reuters) - A Chicago police officer who was sued over the killing of a black man in 2014 has asked a federal judge to sanction the man's mother for making threats against him and his family, a court document said.

George Hernandez shot and killed Ronald Johnson III, 25, in October 2014 while Johnson was running from police. Cook County prosecutors decided on Dec. 7 that no charges would be brought against Hernandez, since Johnson was fleeing arrest and holding a gun.

The Johnson decision came as the nation's third largest city was already rocked by protests over the 2014 police shooting of a black teenager, Laquan McDonald. Officer Jason Van Dyke, who shot McDonald 16 times, was charged with murder late last month

Many protesters have called for the resignation of Mayor Rahm Emanuel over the McDonald shooting. Killings of black men at the hands of mainly white police officers in U.S. cities have prompted a national debate about the use of force by police against minorities.

Johnson's mother, Dorothy Holmes, sued Hernandez and the city in 2014. During a deposition, Holmes secretly took a picture of Hernandez and posted it on Facebook, accompanied by "highly charged derogatory comments," Hernandez' lawyers said in a court motion on Dec. 10.

She also spoke to reporters about how she loved her child as much as Hernandez loves his own teenage children, adding "What goes around comes around... If he wanna take it as a threat, it was a threat," the motion said.

Lawyers for Hernandez said that judicial intervention "is necessary to prevent this kind of conduct as it represents an extremely serious threat for the Hernandez family."

Lawyers for Holmes were not immediately available for comment on Wednesday. Hernandez' picture has appeared on posters at protests, with the word "Murderer" and what appears to be a red handprint on it, according to a court exhibit.

A support rally for Holmes was planned for Wednesday afternoon at City Hall, hosted by Black Lives Matter Chicago.

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"We cannot stand by and allow lawyers for the City of Chicago to harass and 'sanction' a grieving, justice-driven mother in our name, with our tax dollars!" the Facebook post for the rally said.

The U.S. Justice Department this month launched a civil rights investigation into the Chicago Police Department to examine its use of deadly force, among other issues.





(Reporting by Mary Wisniewski and Justin Madden; Editing by Andrew Hay)