Would you mind explaining what mistake did the Bitfinex hack perpetrators do? My understanding is that they were caught when they spent a bit of the money [0]. Because the transaction was on the public ledger FBI knew which wallet to track-which they did and the first few transactions gave the perpetrators away. But then again this is just my understanding. Thanks!

[0] https://en.wikipedia.org/wiki/2016_Bitfinex_hack#Laundering