The video takes your breath away.

It shows a figure, identified by prosecutors as 17-year-old Laquan McDonald, felled by gunfire as he walks away from a line of Chicago police cruisers.

McDonald writhes on the ground as a police officer continues to shoot. At one point, another officer steps close enough to kick what prosecutors say is a knife out of McDonald's hand.

It doesn't square with the story a police union spokesman told at the scene Oct. 20, 2014, the night McDonald died after being shot 16 times by Officer Jason Van Dyke.

FOP spokesman Pat Camden said McDonald was shot in the chest after he lunged at Van Dyke and his partner with a knife. "He is a very serious threat to the officers, and he leaves them no choice at that point to defend themselves," Camden said that night.

"When police tell you to drop a weapon, all you have to do is drop it."

Van Dyke was charged Tuesday with first-degree murder. Prosecutors said Van Dyke opened fire about six seconds after exiting his SUV; he emptied his 9 mm handgun in 14 to 15 seconds; he was reloading it when another officer told him to hold his fire.

A dashboard camera in one of the police cars captured the scene, including several seconds of McDonald lying crumpled in the road. Besides being hit in the chest, he was shot in the scalp, neck, elbow, leg, arms, hand and back.

Cook County State's Attorney Anita Alvarez said the video is unlike anything she has seen in three decades in law enforcement. She predicted it would "tear at the hearts of all Chicagoans."

It does.

The images are so disturbing that the City Council, acting on the recommendation of Mayor Rahm Emanuel's top attorney, approved a $5 million settlement in April before McDonald's family even filed a lawsuit. The city fought for months to delay showing the video to the public. But a judge ordered it released.

That prompted Alvarez to move forward with the charge against Van Dyke on Tuesday, instead of waiting for federal authorities to complete a parallel investigation.

So now we've seen it. It is, as promised, staggering. City officials pleaded for calm as police braced for a long night. The protests had begun even as city officials were preparing to release the video, with a small group demonstrating outside the Burger King in the neighborhood where McDonald was shot.

They called for police Superintendent Garry McCarthy to be fired, for Emanuel to resign. The Rev. Jesse Jackson said Alvarez had taken too long to file charges and called for her to step down.

We share the protesters' anger. We understand their urge to hold public servants accountable. We expect them to make their voices heard. But it will take more than protests, more than the criminal prosecution of a single cop to repair the often fractious relationship between Chicago's police and its people.

This isn't about a stunning, isolated event. Zoom out, and it's part of a broader nationwide clamor over the use of lethal force by white cops against black suspects. Zoom in, and it's about Chicago's long-standing failure to deal effectively with rogue police officers.

Think back to the decades of systematic torture of suspects at the hands of Cmdr. Jon Burge and his crew, as prosecutors and police supervisors looked the other way. That stain will be with us for a long, long time.

But the city also has a poor record for dealing with everyday allegations of police misconduct, from unprofessional behavior to unnecessary force.

A Chicago Tribune review of four years' worth of complaints against police officers found that just over 4 percent were sustained, and in nearly half of those cases, the officer was given a reprimand or a "violation noted." That's it.

Some - perhaps most - complaints can't be proved. But the process is also hamstrung by union rules about how complaints are investigated and appealed. That explains, for example, why Van Dyke remained on paid desk duty for 13 months before he was charged with a crime. "We don't have at-will employees, and we can't just fire them as people expect," McCarthy reminded reporters at a Tuesday news conference before the video was released.

The Independent Police Review Authority, the civilian board that handles the most serious cases, doesn't take into account previous complaints against the same officer when investigating a new one. In the Tribune's analysis, 11 officers racked up a combined 253 complaints that resulted in a single five-day suspension. Come on. What does it take to flag a problem cop?

The system should have identified Van Dyke as a ticking time bomb. IPRA records show he was named in 17 citizen complaints - including three alleging excessive force - since 2006. All but two of them have been resolved, and none resulted in discipline.

Now, he's facing a first-degree murder charge.

It's not enough for Emanuel and McCarthy to urge calm. It's not enough to talk about the increased training and supervision that McCarthy says have dramatically reduced the number of police shootings on his watch. The mayor and his police chief must commit to a thorough examination and overhaul of the disciplinary process. That must come with a pledge for greater transparency, so the public can see for itself how complaints against cops are resolved.

Police officers deal with dangerous situations every day. But Chicago's history of slow or no disciplinary action creates the impression that misconduct goes unpunished. That has to change. The city must make good on its promise to put cameras in every cruiser and on every cop. And it must stop trying to hide those recordings from the public.

If not for the video, it's unlikely that Van Dyke would be facing a murder charge. Chicago wouldn't be having this important discussion.

In the coming days, that video will be viewed again and again. It will send citizens into the street - peacefully, we hope - and keep them up at night. Those images are deeply disturbing. Chicago needed to know exactly what happened.