It was an inside job. It had to be.

And the Chicago Police Department had better get to the bottom of it.

EDITORIAL

It is bad enough that our city is awash with illegal guns. But to think that the cops themselves might be the source of some of those guns — or of even one. That would be a new low. The onus is on Police Supt. Eddie Johnson to solve this one or watch the public’s trust in our local police crumble just a little more.

Five years ago, according to a Better Government Association report in Sunday’s Sun-Times, a handgun turned up next to the body of a gang member who was shot to death by a Cicero police officer. Whether the gun belonged to the young man or was planted by the Cicero cop seems to be a matter of dispute, but what is clear is that the gun once was in the custody of the Chicago Police — and it was supposed to have been destroyed.

Thirteen years ago, a Cook County judge, William Stewart Boyd, had turned the gun over to the Chicago Police as part of a buyback program meant to take weapons off the street. Judge Boyd turned in the gun, a .38-caliber Smith & Wesson, and received a prepaid Visa card worth something less than $100.

As the BGA reports, the Chicago Police recover thousands of guns each year through buybacks, and confiscate thousands more when making arrests. The guns are supposed to be destroyed. But the gun the judged had turned in mysteriously popped up again in Cicero, at the scene of the shooting of 22-year-old Cesar A. Munive.

That shooting has a particularly bad feel about it. The Cicero police officer had a history of disciplinary problems, the victim’s family claimed in a civil rights suit that the officer shot an unarmed man, and the Cicero Town Council voted a few weeks ago to pay the family $3.5 million to settle the case.

But our question today has to do with the gun. How did it go from Chicago Police custody in 2004 to the scene of police-involved shooting in 2012?

When the police take a gun off the street, you would like to believe its killing days are over.

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