How did Baltimore police officers avoid significant oversight and reform despite years of allegations of brutality? A new report puts the blame on big restrictions set by Maryland state law and Baltimore's contract with a major police union.

In the report, Samuel Walker, a criminal justice expert from the University of Nebraska at Omaha, analyzed the Baltimore Police Department's contract with the Fraternal Order of Police and the Maryland Law Enforcement Officers' Bill of Rights. The report details various examples of how the police union contract and state law prevent accountability — usually by adding bureaucratic barriers and imposing technical requirements that make it fairly difficult to conduct a speedy, thorough investigation into alleged misconduct.

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The lack of accountability not only makes it difficult to prevent police abuse and build trust between locals and law enforcement, but it can actually make it more difficult for honest, good cops to do their jobs. "Trust and legitimacy lead to greater cooperation with the police by community residents," Walker writes. "That cooperation takes the form of reporting crimes, reporting neighborhood problems, providing information about suspected criminal activity, and a greater willingness to serve as witnesses in criminal cases."

Here are six of Walker's findings, taken from the 11-page report.

1) Investigators may be forced to wait 10 days after a shooting to interrogate a Baltimore police officer

The Maryland Law Enforcement Officers' Bill of Rights permits a 10-day delay in any interrogation of a police officer involved in a matter that could require discipline.

As Walker notes, this conflicts with widely accepted best practices established by the Justice Department that require police officers to be interviewed as soon as possible following a shooting or use-of-force incident that causes an injury. He also notes that the 10-day delay could ruin an investigation, because it gives officers more time to possibly conspire with others, including fellow cops, to fabricate a story.

2) Police misconduct can't be scrutinized by citizen review boards

The Maryland Law Enforcement Officers' Bill of Rights requires that Baltimore police officers be interrogated only by another sworn officer — or the state attorney general, or a designee if requested by the governor.

The problem with this requirement, Walker writes, is that it essentially prohibits civilian oversight, which was suggested by the President's Task Force on 21st Century Policing and can help build trust in the community toward police.

3) Hearing boards require at least one peer officer as a voting member

The Baltimore police union contract, a regularly renewed three-year pact, requires that a three-person hearing board is established in cases involving officers misconduct, and one of the members of the hearing board must be a peer officer of the same rank as the cop under investigation.

But Walker says hearing boards should be required after the police chief imposes discipline in a case — to give officers a chance to appeal discipline decisions but also maintain some of the chief's independence. He also argues that requiring an officer who's the same rank as the cop being investigated may skew a vote for disciplinary action — if the police officer sympathizes with his coworker.

4) Baltimore police officers can have their records of alleged misconduct expunged

Police officers can have allegations of misconduct stripped from their records if they are "not sustained, exonerated, unfounded."

That might seem innocent enough, considering the allegations were never proven. But Walker notes this violates established best practices in law enforcement and makes it much more difficult to detect a pattern of misconduct among individual officers.

"The basic principle is that an [early intervention system] should capture the most complete picture of an officer's performance," Walker notes. "Most citizen complaints are not sustained, but it is a revealing indicator of an officer's performance if an officer receives complaints at a much higher rate than peer officers."

5) Baltimore cops can't be fired "solely" because they've been marked as having problems with "credibility, integrity, or honesty"

The Baltimore police union contract and Maryland law prohibit the police department from firing, demoting, suspending without pay, or cutting the salaries of officers "solely" because they've been placed on "witness do not call" lists maintained by the state's attorney for Baltimore, which tracks officers "who have been found or alleged to have committed acts which bear on credibility, integrity, honesty, or other characteristics that would constitute exculpatory or impeachment evidence."

Walker calls this "unbelievable." "A police officer who has been determined to have performance problems related to 'credibility, integrity, or honesty' should not be retained by the department," he writes. "Police officers possess the awesome power to deprive people of their liberty through arrest and to take human life. The highest standards of integrity and honesty must be expected of all officers. On one specific point, an officer on the 'do not call' is, according to the language of the police union contract, unable to serve as a witness in a criminal case. And if an officer cannot serve as a witness in a criminal case, he or she cannot make arrests."

6) Notices of disciplinary actions can't be made public

The Baltimore police union contract prohibits the department from making notices of disciplinary actions public.

This not only makes it difficult to hold individual cops accountable, but Walker notes that this offers greater protections to cops than some private employees receive. "In many, if not most or all states, the discipline of lawyers and medical professionals are public record," Walker writes. "And it is worth remembering that most members of those professions are private and not public employees. Why should police officer, who are by definition public employees, enjoy this special shield from accountability?"

So it's difficult to hold Baltimore police officers accountable — and even when they are punished, the public may never know about it.