Look, from my PoV its fairly simple. When the police go to arrest a suspected murderer, they roll deep.
When they go after an alleged copkiller, its like someone broke out a beehive.
Here, the alleged FBI are showing up with 3 dudes and knocking on the door for a case where they claim they have Dresden on camera and his fingerprints as well(we'll get back to prints, and how they got them from a dead body that got dumped in a lake, in less than a couple hours, given how long it takes forensics)
All feds. No locals. No backup.
Its so patently ridiculous that Im halfway convinced that if we had access to any police database and scanned for the faces of these fellows, they'd have criminal records.
Getting Clippy to search for their faces on Facebook/Myspace/social media and the like might be worth doing.
They said they had video.
That immediately limits where it could have allegedly happened, since there arent that many places with electronically recorded video in 2006. And there are no federal lands in and around Chicago for FBI jurisdiction to apply.
And the dead give away here: three men.
Look at any police response to an alleged cop killer in the US; they're literally swarming all over the place, like a gang.
And the FBI would not attempt to arrest a copkiller without more people or more local backup.
Also worth noting that Dresden remembers the FBI hexenwulfen.