Some exchanges make it particularly difficult to follow. With Kraken you can generate a key every time you want to transact. I think that is quite untraceable, but I would like someone with good knowledge to show me I am wrong.
From a legal standpoint with that, a court in their country can order the information from them which can then be used for prosecutions if that's helpful. It's probably easier for some courts to use state-funded hackers to try to get into the exchanges and link the addresses though. I assume there is a link between these addresses to see the previous ones you have used on that exchange.
There might also be the issue that the funds are all sent from the same address to a different address that end up in the Kraken's main address (in their cold storage normally).
I mean, untraceable as far as being able to trace it directly to an Eth account or user. I do not consider legal requirements, and I definitely do not consider hacked evidence as suitable for most governments or legal systems.