After internal affairs or the ACU identifies an egregious offender, it's far from certain the department brass will be able to adequately punish him. "It's not a question of whether the department wants to fire someone," Mancini said. "It's a question of can they." BPD leaders say one of the biggest hurdles to cleaning up the force is the state's Civil Service Commission, an independent body established in 1884 to prevent politicians from interfering in the hiring practices of public agencies, or managers from canning people unfairly. The governor-appointed commission is currently made up of three full-time members and two part-timers, with its chairman, Christopher Bowman, earning roughly $90,000 a year. Any police officer—or civil servant—who has been disciplined or fired can appeal to the commission and have a full hearing. If it decides the cop was wrongfully dismissed, it can overrule the firing unilaterally. That's a crucial difference from the way things are done in New York, for example, where the police commissioner has the final say.

Bowman points out that the commission sides with the police agency roughly 85 percent of the time. "We don't impede the ability of a police department to discipline a cop for just cause," he says. "We are not biased. We're a check-and-balance on the system." Still, the Massachusetts Major Cities Chiefs, an association of top cops from across the state, lists elimination of civil service protection for police as a critical mission. History is not on the reformers' side: Both Mitt Romney and Bill Weld launched attempts to overhaul the commission, and both failed miserably, because legislators didn't want to anger the state's public employee unions.

Regardless of how often the commission rules in favor of the BPD brass, the mere threat of an appeal is often a deterrent to disciplinary action. Davis cites civil service protection as preventing him from firing David Murphy after the cop was charged with punching his girlfriend in the face at a Baltimore bar. Davis weighed moving to kick Murphy off the force, knowing that if he did, Murphy almost certainly would appeal to civil service. The BPD's legal department told Davis the fight could stretch on for years, cost tens of thousands of dollars, and most likely be "a loser," Davis says, because Murphy had agreed to probation before judgment (meaning his record won't show a criminal conviction if he stays out of trouble during his 18-month probation). So instead, Murphy is back on the force, making him one of 11 Boston cops suspended by the department for domestic violence allegations over the past two years who got to keep their jobs.

The case of Michael LoPriore illustrates a further layer of protection for cops, no matter how badly they perform. In 2004, LoPriore was investigated for allegedly forging signatures on detail slips, defrauding taxpayers of more than $1,100. And that was two years after he got caught using a police cruiser to pick up a drunken woman outside a bar and deposit her in Charlestown without radioing in that he was transporting a civilian. Yet neither of those offenses was enough to get him fired, not after the Boston Police Patrolmen's Association got involved on his behalf. It wasn't until LoPriore forced a 19-year-old Chinatown prostitute to have sex with him in his car (with his child's car seat strapped in the back), that serious action was taken. During the encounter, the hooker snatched LoPriore's badge while his pants were around his knees. She went to the FBI, who bugged her phone in the hopes that he'd call to get his badge back—which he did. This time the union stayed out of it, and LoPriore was forced to resign. But for the department, it was too late: It had already suffered another major embarrassment.