This sort of thing keeps happening, and explains why the police hate the public's ubiquitous video recording:
When CTA supervisor Martesa Lee attempted to lodge a complaint against a Chicago police officer in February, she was given a choice:
Drop her grievance against the officer she accused of pushing her out of an unmarked crime scene on a Red Line platform or face possible arrest.
“Is it worth it to you?” Chicago police Sgt. William Spyker asked her.
Authorities arrested Lee in front of her co-workers and a platform of CTA riders after she informed the sergeant she would not let the matter go. With her hands cuffed behind her back and tears streaming down her face, she refused additional opportunities to retract her grievance and regain her freedom.
Looking at the facts in the light most favorable to the police, I see no reason to arrest Lee. The time to arrest her for "obstruction of justice" would have been as she actually entered the active crime scene—but even then, it seems clear why the officer chose to let her go.
Spyker's instinct was to arrest someone who disagreed with him, who threatened to make someone on his team fill out some paperwork. He made a blatant argument to force: do this or I will inflict physical violence on you. "Spyker raised the specter of arrest within 35 seconds of Lee approaching him with her concerns," the Tribune pointed out. Despite Spyker's calm demeanor in the video, I'm guessing he didn't have a lot of other tools to use in resolving this dispute.
In fact, "it’s unlikely Haran would face discipline for removing Lee from the crime scene as he has a responsibility to protect the scene’s integrity," one source told the reporter, meaning that all Spyker had to do was take down the complaint and move on with his day. The body cam footage of Lee's initial confrontation with the police is murky at best about who was at fault. Spyker's handling of the situation after the fact is what got this into the newspaper.
(The title of this post is from Foundation by Isaac Azimov.)