They’d essentially have to by hand arrest every single node that participated to the source
I may be wrong on this, but I think that’s exactly the risk associated with hosting TOR Exit nodes.
If they bust a darknet server, for example one hosting child pornography, they sometimes end up with logs of every IP that was accessing the said node. IP of every exit node that someone used to route their traffic. And they do investigate, and it will affect your life, even if you are not doing anything illegal - and even that line is pretty blurry in some of the countries.
If that IP is yours, you will get a visit from police. Being accused of anything in regards to child pornography is not a laughing matter. From what I’ve heard, they may take all of your electronics, you will get interogated and you have to prove beyond doubt that you did not know that someone is using your computer - the exit node - for such activites. In some countries, merely enabling someone to distribute or access child porn - which is exactly what an exit node is doing - is illegal. And while TOR has been in the public knowledge for pretty long time, you may get a judge who has never heard about TOR and has to research it for your case. And in addition to that, you are now literally investigated of distributing child porn. If someone finds that out, it will ruin your reputation and history has shown that being accused of something is enough for many people, no matter the result. Good luck explaining to your grandmother how does TOR work, or to HR at your company why you are being investigated for child porn distribution or why they confiscated your company laptop.
In general, running an exit node from your home Internet connection is not recommended, unless you are prepared for increased attention to your home. In the USA, there have been no equipment seizures due to Tor exits, but there have been phone calls and visits. In other countries, people have had all their home computing equipment seized for running an exit from their home internet connection.
So, it esentially boils down to who is handling the investigation of your case. The police can either accept that it’s an exit node and a waste of time and leave you alone, or they can make your life a living hell if they choose to.