The Missouri cop who killed 18-year-old Michael Brown suffered a "serious facial injury," a source close to the officer told ABC News on Wednesday.

Conflicting accounts surround what happened the night Ferguson Police Officer Darren Wilson shot and killed the unarmed teen on Aug. 9. Some witnesses say Brown was running away with his hands in the air when he was shot.

Other reports say Wilson feared for his life during a scuffle with Brown that began when the officer drove up to the teen and his friend while they were walking in the street.

Wilson and Brown struggled by his vehicle, during which Wilson suffered "a serious facial injury," the unidentified source told ABC News. The nature of the facial injury is not immediately clear, but Ferguson Police Chief Tom Jackson said one side of the officer's face was swollen.

Wilson has not yet made any public statements about the shooting.

The news comes the same day a grand jury was scheduled to hear evidence of the shooting, which sparked days of ongoing violent and peaceful protests in Ferguson. Activists called for the cop's arrest and an independent investigation into the death of a black teen at the hands of a white officer.

Tuesday night protests saw 47 people being arrested, including one for the third time, ABC News reported. But the overnight protests were quieter then the last few days, with no smoke bombs or tear gas being used to disperse the crowds.

Attorney General Eric Holder, who is scheduled to travel to Ferguson on Wednesday to meet with FBI officials, promised an independent investigation.

"Our investigation into this matter will be full, it will be fair, and it will be independent," Holder wrote in an editorial in the St. Louis Post-Dispatch.

"And beyond the investigation itself, we will work with the police, civil rights leaders, and members of the public to ensure that this tragedy can give rise to new understanding- and robust action- aimed at bridging persistent gaps between law enforcement officials and the communities we serve."