This Sun-Times editorial provides good background.
It's a bad shooting. (Though honestly I was expecting even worse, like an unarmed rationally behaving victim.) The mayor (now, at least) and the police chief have said the officer is at fault.
The officer who killed McDonald fits the pattern of bad cops: high activity, drug work, too many complaints. Sure, all the complaints weren't justified, but some of them were. And undoubtedly he did a lot of bad shit that people didn't file formal complaints about.
From the Washington Post:
The allegations against Van Dyke include 10 complaints of excessive force, including two incidents where he allegedly used a firearm, causing injury. He was also accused of improper searches and making racially or ethnically biased remarks. Four of the allegations were proven factual, but Van Dyke’s actions were deemed lawful and appropriate. In most of the other cases, there was either not enough evidence to prove or disprove the complaint or the allegation was proven unfounded.68 complaints and a criminal conviction and no disciplinary action?! That is rotten.
The data shows that it’s rare for any officers to be penalized, and white officers were half as likely as black ones to be disciplined for a complaint.
Apparent repeat offenders — officers with more than 10 complaints against them — represented 30 percent of all complaints, even though they made up only 10 percent of the police force.
That distinction [the most complained-about officer] goes to Jerome Finnigan, the subject of 68 citizen complaints in nearly two decades with the Chicago Police Department; none of the allegations resulted in disciplinary action.
In 2011, Finnigan was convicted of robbing criminal suspects while serving on an elite force and ordering a hit on a cop he thought might turn him in. At his sentencing, Finnigan admitted to having become “a corrupt police officer,” according to the Chicago Tribune. But he said the police department was aware, and for many years did nothing.
“My bosses knew what I was doing out there,” he said, “and it went on and on. And this wasn’t the exception to the rule. This was the rule.”
So this cop shows up on a scene and, rather than doing nothing, gets out of his car, puts himself almost in harm's way, and kills this guy. And then keeps firing. Fires 16 shots. No other cop saw a need to shoot. Because there was no need to shoot. You contain, retreat, or make do. Then you tase this guy. Or what about having shields and a straight baton?
Anyway, will Chicago riot like Baltimore? No. For two reasons. First of all there is now legal accountability. That's the way the system is supposed to work. You murder somebody? You face justice. Second, unlike Baltimore Mayor Rawlings-Blake and former Police Commissioner Batts, the political and police leadership in Chicago have a minimum level of basic competency.
Update: Here's the initial account (hat tip to Chris Hayes)