What they (Seattle Police Department) claim to have was a tip, from 4chan, filtered through a national clearinghouse, that about seven weeks prior someone had allegedly transferred to 4chan a video of an unidentified woman abusing an unidentified child in an unknown location at an unknown time, allegedly from an IP address that they discovered was assigned by an ISP to David and that they learned prior to the search was the exit point from an anonymizing proxy network.
SPD staff involved were familiar with Tor and thus knew that there was no more reason to suspect David--an outspoken critic of their public surveillance programs and other privacy-invading programs--of uploading the evidence of some woman's crime to 4chan than to suspect any of the many thousands of users of the Tor network of such. This was pure harassment.
Would they raid a Starbucks if someone used Starbucks wifi to distribute CP? No, they would need more evidence that someone at that Starbucks was doing it and not just someone who bought a cup of coffee there that day.
Tor is open wifi, the IP of the exit node doesn't provide evidence that the person running the exit node has anything to do with the traffic.
That's why they raided his house.
> Would they raid a Starbucks if someone used Starbucks wifi to distribute CP?
Of course they would. Obviously aiming to try and catch the perpetrator in the act, but also at least to get a good look at the network configuration.
"CP came from this IP endpoint" means crime is being committed using this network. It's perfectly reasonable for them to go and investigate. And as others point out, them knowing how Tor works makes no difference - otherwise people making/distributing CP would host their own exit nodes with the sole purpose of being able to point them out to police and tell that CP it's not their traffic.
They didn't jailed him, they checked if he is in fact involved - and finding no additional evidence, left him in peace.
If you take anything but a ridiculously short term view, the expectations of how police will treat people today are far higher than they have been in the history of the US.
We still have to recognize and confront the remaining problems, but national media attention and prosecution of police who commit murders is a step up from police committing murders with no consequences.