Realistically, unless there is a core router going throuhg somehwere like north korea, and they can manipulate the traffic, before it leaves, all traffic can be traced source to end point in some way, as these routers are just passing the 1'0s from your computer to the destination, or vice versa, but each has address in it. I really think that a bad actor inside cisco, or a hacker of cisco firmware, that goes undetected for years would be the best type of realistic, but finctional story. The only problem with hiring a pi would be that they wouldn't have the permissions, in all the different jurisdictions. It would have to be, europol or something, and that doesn't oeprate everywhere obviously.
A normal pi would never be able to trace things through the internet meaningfully past borders. A myssterious hooded retired black hat hacker that used to work as an insider to a small company in the cogs infrastructure of between the routers, and the domain ownership icaan maybe could, lol
I hope when you release your series, you buy a jrvip membership here and advertise in your sig, your ebooks! lol they will make for good reading, as your the dude that always asks the funny "how did bitcoin...." questions?

You doing some homework for real! lol