THERE’S been a cover-up in Chicago. The city’s leaders have now brought charges against a police officer, Jason Van Dyke, for the first-degree murder of 17-year-old Laquan McDonald. But for more than a year, Chicago officials delayed the criminal process, and might well have postponed prosecution indefinitely, had it not been for a state court forcing their hand.

They prevented the public from viewing crucial incriminating evidence — first one police car’s dashboard camera video; now, we learn, five such videos in total. And these senior officials turned a blind eye to the fact that 86 minutes of other video surveillance footage of the crime scene was unaccountably missing.

The Cook County prosecutor, Anita Alvarez, must have had probable cause to indict Officer Van Dyke for the Oct. 20, 2014, shooting death of Mr. McDonald the moment she viewed the police dash-cam video, after her office received it two weeks later. That video, in her own words, was “everything that it has been described to be by the news accounts. It is graphic. It is violent. It is chilling.”

Ms. Alvarez, and other city leaders, surely knew they would have to indict Mr. Van Dyke for murder as soon as the public saw that footage. “I have absolutely no doubt,” Ms. Alvarez finally said last week, “that this video will tear at the hearts of all Chicagoans.”