Recently a man was deceived by someone who had change the electrum source code on an old version of it. He lost 1400BTC(!)

I had made a similar question in the past, but the answer didn't satisfy me. Why should that hacker use a mixer? If he try to sell the bitcoins from his main address (the one with the 1400BTC) he will get caught, because he will prove that he is the hacker.

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.