The announcement Tuesday that three officers have been charged with lying about that night raises questions about why it took so long to bring charges and underscores how tough it is to battle the code of silence long associated with the Chicago Police Department and other law enforcement agencies across the country.

"Even though the police brass had seen this video, knew what was on it, each of the reports of these officers was approved all the way up the chain of command," said Craig Futterman, a University of Chicago law professor who has studied the department and was part of the legal team that fought the city over its refusal to release the video.

The officers who knew there was a video, he said, knew they could lie because "the CPD has allowed that for far too long."

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