By Alex Dobuzinskis

(Reuters) - An Illinois judge on Thursday appointed a special prosecutor in the murder case against a white Chicago police officer in the shooting death of a black teenager, selecting a state's attorney from a neighboring county.

Cook County Judge Vincent Gaughan announced the appointment of Kane County State's Attorney Joseph McMahon at a hearing, Anne Kavanagh, a spokeswoman for the officer's attorney, said by telephone.

McMahon will bring the first-degree murder case against Chicago police officer Jason Van Dyke in the 2014 killing of 17-year-old Laquan McDonald, which made national headlines and sparked protests after the release of a video of the shooting last fall.

It showed the officer shooting McDonald 16 times as he jogged away from police cars. Authorities said McDonald was armed with a knife and had slashed at the tires and window of a patrol car.

The appointment of McMahon allows the politically sensitive case to move forward. Cook County State's Attorney Anita Alvarez had recused herself and asked the judge to appoint a special prosecutor.

Alvarez lost her re-election bid in March after protests over her taking a year to charge Van Dyke. She charged him the same day video of the shooting, taken from the dashboard of a patrol car, was released by order of a judge.

Van Dyke's attorney has said the officer feared for his life when he opened fire, while prosecutors have argued the shooting was not justified.

McMahon, a Republican, is seeking re-election to his post in Kane County.

When he launched his campaign last year, McMahon stressed his aggressive prosecution of violent crimes and his support for rehabilitation programs for offenders who are not violent, according to a report at the time in local newspaper the Elgin Courier-News.

The shooting of McDonald came at a time of heightened national debate over police use of deadly force, especially against black men.

The judge has imposed a gag order in the case.

McMahon, speaking outside of court under a special authorization from the judge, told reporters Van Dyke is presumed innocent until proven guilty.

"I and (my) team has one goal in this case, that is to find the truth, to present the truth and ask that justice be served in this case," McMahon told reporters.

Criticism of the way officials handled the McDonald shooting led to the firing of Chicago's police chief and calls for Mayor Rahm Emanuel to resign.

(Reporting by Alex Dobuzinskis in Los Angeles; Editing by Dan Grebler and David Gregorio)