FYI, I've added an update in the comments to my original article at:
https://hasbrouck.org/blog/archives/002292.html
I finally spoke with United Airlines spokesperson Charlie Hobart today, after this article was published.
Mr. Hobart told me that the gate agents handling United Express flights at O'Hare, including those who called in what Mr. Hobart described as "Chicago Department of Aviation security officers", were employees of United and not of Republic or a third-party contractor.
Mr. Hobart claimed not to know whether or not "CDA security officers" are sworn law enforcement officers. That claim to ignorance strains credulity, unless United has deliberately kept its own spokespeople in the dark. And if United still hasn't been able to figure out, 10 days later, whether these thugs (I use that term deliberately, in its original sense of organized gangs that prey specifically on vulnerable travellers) were really police, how were passengers supposed to figure that out in the moment?
"I don't have access to that level of detailed information," he said in response to this and most of my other questions. When I asked if he could find out, he declined. "I'm not going to get into that level of detail."
Mr. Hobart said he didn't know whether the passenger was asked to leave by United or Republic employees, whether the "officers" were asked to remove the passenger by United or Republic employees, whether the officers talked to the pilots before removing the passenger, or how the officers identified themselves to the passenger.
"They were unable to obtain the cooperation of the passenger," Mr. Hobart said. He referred all my other questions to the City of Chicago Department of Aviation.