Bottom line: Seemingly having exhausted all other options in its four-year-old investigation, cryptocurrency exchange Bitfinex is now hoping that someone will come forward with fresh tips or perhaps appeal to the hackers' guilty conscience. Eh, good luck with that.

Bitfinex on Tuesday put out a call to the cryptocurrency community to help in the recovery of nearly 120,000 Bitcoins stolen from the exchange more than four years ago.

In early August 2016, hackers breached the exchange's security systems and initiated 2,072 unauthorized transactions, resulting in the theft of 119,755 Bitcoins. The heist was valued at around $70 million at the time but today, those stolen coins are collectively worth nearly $1.35 billion.

Understandably, Bitfinex would like them back.

The exchange today said that anyone who puts them in contact with the hacker(s) will receive five percent of the total property recovered (or equivalent funds or assets at current market values). But here's where it gets interesting - Bitfinex is offering the hackers themselves 25 percent of the total property recovered if they return the funds on their own.

In total, Bitfinex said it is prepared to hand over around $400 million in rewards.

In order to confirm the identity of the hackers, we will request that 1 Satoshi is sent from the wallet address responsible for the hack to a wallet address specified by Bitfinex. We will work to ensure this can be done safely, thereby protecting the identities of all parties, and Bitfinex reserves the right to impose conditions on any transfers in order to verify claims and ensure a secure process.

Bitfinex said it has worked with law enforcement on the investigation since the start but have only managed to recover fewer than 28 of the stolen Bitcoins over the past four years.

Masthead credit: Tom Stepanov