If he send 1BTC to 1400 owned addresses, though, no one can prove that the person that owns those 1400 addresses is the hacker, right? They can only ask them where did you get that one bitcoin.
When there's an investigation the authorities will trace all the transactions especially the amount involve is a significant amount.
If the hacker send the hack BTC to an exchange where he slowly withdraw according the limit using a non verified account then the exchange would never know if who owns the bitcoin, however, there are always a trail since everything goes to the blockchain and the exchange knows the transaction.
If the hacker then will send the btc to a mixer, then I would say it's hard to find but it's not impossible since like I said everything goes in the blockhain and I don't know if it's possible for a mixer to cooperate with the authorities.