“This is the story of the revelation in late 2013 that Bitcoin was, in fact, the opposite of untraceable—that its blockchain would actually allow researchers, tech companies, and law enforcement to trace and identify users with even more transparency than the existing financial system.”
The main way criminals are caught is when they transfer their crypto to an exchange so they can convert it to cash. Law enforcement will subpoena the exange and ask “Hey, who exchanged 0.7886 bitcoin for cash on this date?” and they will get their identity. Using the public ledger, they will be able to trace the transactions done and show that this person sent money to an address advertised as belonging to a trafficking site, an illegal market, or recieved money from the bad wallet address.
The address owner is anonymous until there is a source of data that ties information the wallet, and often transactions can be used to do that, just as any way to advertise a wallet belongs to you can, or any way to exchange crypto to cash can.