Demonstrators protest outside the Ferguson, Missouri, police department during the National March on Ferguson, August 30, 2014. (Michael B. Thomas/AFP/Getty Images)

What happened in Ferguson, Mo., last month was a tragedy. What’s on course to happen there next month will be a farce.

October is when a grand jury is expected to decide whether to indict the white police officer, Darren Wilson, who killed an unarmed black teenager by firing at least six bullets into him. It’s a good bet the grand jurors won’t charge him, because all signs indicate that the St. Louis County prosecutor, Robert McCulloch, doesn’t want them to.

The latest evidence that the fix is in came this week from The Post’s Kimberly Kindy and Carol Leonnig, who discovered that McCulloch’s office has declined so far to recommend any charges to the grand jury. Instead, McCulloch’s prosecutors handling the case are taking the highly unusual course of dumping all evidence on the jurors and leaving them to make sense of it.

McCulloch’s office claims that this is a way to give more authority to the grand jurors, but it looks more like a way to avoid charging Wilson at all — and to use the grand jury as cover for the outrage that will ensue. It is often said that a grand jury will indict a ham sandwich if a prosecutor asks it to. But the opposite is also true. A grand jury is less likely to deliver an indictment — even a much deserved one — if a prosecutor doesn’t ask for it.

One might give McCulloch the benefit of the doubt, if not for his background. His father was a police officer killed in a shootout with a black suspect, and several of his family members are, or were, police officers. His 23-year record on the job reveals scant interest in prosecuting such cases. During his tenure, there have been at least a dozen fatal shootings by police in his jurisdiction (the roughly 90 municipalities in the county other than St. Louis itself), and probably many more than that, but McCulloch’s office has not prosecuted a single police shooting in all those years. At least four times he presented evidence to a grand jury but — wouldn’t you know it? — didn’t get an indictment.

One of the four: A 2000 case in which a grand jury declined to indict two police officers who had shot two unarmed black men 21 times while they sat in their car behind a Jack in the Box fast-food restaurant. It was a botched drug arrest, and one of the two men killed hadn’t even been a suspect. McCulloch at the time said he agreed with the grand jury’s decision, dismissing complaints of the handling of the case by saying the dead men “were bums.” He refused to release surveillance tapes of the shooting. When those tapes were later released as part of a federal probe, it was discovered that, contrary to what police alleged, the car had not moved before the police began shooting.

McCulloch apparently hasn’t learned from that. His spokesman, asked by The Post’s Wesley Lowery about those remarks, said the slain men “should have been described as ‘convicted felons’ rather than ‘bums.’ ”

Lowery gained national attention last month when he was unjustly detained by Ferguson’s out-of-control police while covering the demonstrations. He has since asked McCulloch’s office for a list of cases in which prosecutors pursued charges against a law enforcement official. McCulloch’s office ultimately came up with only one case over 23 years that The Post could verify of the prosecution of a white officer for using inappropriate force against a black victim, and it wasn’t a shooting.

But if McCulloch lacks credibility, he apparently has political clout. This could explain why Missouri Gov. Jay Nixon — like McCulloch, a Democrat — is refusing to appoint a special prosecutor. This could also explain Democratic Sen. Claire McCaskill’s statement in support of McCulloch.

Proving a case of excessive force against a police officer is difficult, and I’m not in any position to determine Wilson’s guilt. But that doesn’t justify declining to prosecute such cases. There’s no dispute that Brown ran away after Wilson shot him in a scuffle and that Wilson shot Brown several more times after that. Several witnesses — including those in a newly discovered video showing the immediate aftermath of the shooting — claim that Brown had his hands up in surrender. The alternative account offered by Wilson — Brown charged at him — requires us to believe that the unarmed and wounded man ran away, reconsidered and ran back toward the man pointing a gun at him.

And McCulloch won’t have his prosecutors recommend even involuntary manslaughter? If he persists and if the governor won’t intervene, their behavior will confirm suspicions that justice is rigged.