Maybe by using one of the sophisticated blockchain analysis programs that now exist. They don’t need millions of years.
Here are a couple of articles to start you off.
This one has an example of tracing back transactions through a number of intermediate anonymous addresses:
In the early days, criminals used Bitcoin as a safe haven, thinking Bitcoin is anonymous, and transactions can’t be traced. However, today, sophisticated blockchain analysis softwares can trace bitcoin transactions to identify criminal activities on the blockchain.
Here’s a list of some analysis software:
… To accomplish this, Yum followed more than 700,000 bitcoins on the blockchain, from the Silk Road marketplace to Ulbricht’s personal wallets. It was the first time people realized the potential of blockchain analysis to solve a criminal investigation.
Today, blockchain analysis technology is used by financial institutions, crypto businesses, and law enforcement authorities to prevent and investigate cryptocurrency crimes worldwide.