A federal investigation that cleared a Ferguson, Missouri, police officer for killing Michael Brown concluded that the physical evidence and credible witnesses all bolster the officer's account that he feared for his life when he fatally shot the black 18-year-old.

The Department of Justice released an 86-page report Wednesday summarizing its reasons for not charging former officer Darren Wilson, who is white, with a federal civil-rights violation for the Aug. 9 shooting that sparked protests in the St. Louis area and across the nation.

"Based on this investigation, the Department has concluded that Darren Wilson's actions do not constitute prosecutable violations," the federal report said.

That mirrors the determination of a St. Louis County grand jury, which decided in November not to bring state criminal charges against Wilson. Here's a look at some of the key findings in the federal report:

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ROBBERY SUSPECT

Wilson first encountered Brown and his friend, Dorian Johnson, walking in the middle of a Ferguson street, just minutes after a report of a robbery at a nearby convenience store. According to Wilson's testimony, after he told the two to move out of the street, he realized they matched the description of the robbery suspects. The Justice Department report says that police dispatch recordings and Wilson's radio transmissions show that he was aware of the theft and had a description of the suspects as he encountered Brown, who was carrying stolen cigarillos.

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VEHICLE STRUGGLE

After the initial encounter, Wilson backed up his police vehicle and confronted Brown. A struggle ensued. The Justice Department report says that Wilson and other witnesses stated that Brown reached into the police SUV through an open window "and punched and grabbed Wilson." The report says that is "corroborated by bruising on Wilson's jaw and scratches on his neck, the presence of Brown's DNA on Wilson's collar, shirt and pants, and Wilson's DNA on Brown's palm."

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GRABBING FOR GUN

Wilson has testified that Brown reached for his gun during the struggle in his vehicle. The report says Wilson fired two shots from the vehicle. Brown was shot in his hand. The federal report says autopsy results and the trajectory of the bullets back Wilson's account. It says skin from Brown's palm was found on the outside of the police SUV door, and Brown's DNA was also found on the inside of the driver's door. That would "corroborate Wilson's account that during the struggle, Brown used his right hand to grab and attempt to control Wilson's gun," the report says.

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HANDS UP

After the initial shots, Brown ran away from Wilson's vehicle. The Justice Department report says Brown was not shot in the back, because there were no entrance wounds there. At some point, Brown stopped and turned around. Some witnesses have said Brown had his hands up in a sign of surrender — an assertion that became popular among protesters. The federal report notes that there are varying accounts of what Brown was doing with his hands. But the report concludes: "There are no credible witness accounts that state that Brown was clearly attempting to surrender when Wilson shot him."

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CHARGING BACK

Wilson has testified that after Brown stopped running, he turned around and began charging back toward the officer. Wilson said he feared for his life as he then fatally shot Brown. The federal report says that all the credible witness accounts "establish that Brown was moving toward Wilson when Wilson shot him." The report says the physical evidence — namely, blood stains on the road — also confirms that Brown moved toward Wilson after he turned to face them.

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Follow Holbrooke Moore and David A. Lieb on Twitter at https://twitter.com/holbrookmohr and https://twitter.com/DavidALieb .