Cryptocurrency investors in South Africa may have lost nearly $3.6 billion in Bitcoin following the disappearance of two brothers associated with one of the country’s largest cryptocurrency exchanges. According to Bloomberg, a law firm in Cape Town says it can’t locate Ameer and Raees Cajee, the founders of Africrypt. In April, the exchange told its investors it was the victim of a hack and asked them not to report the incident to the authorities on account it would “slow down” the process of recovering their missing money.

Some of those involved in the exchange hired Hanekom Attorneys, the law firm that said it couldn’t find the two brothers, to investigate the incident. It found that someone had withdrawn Africrypt’s pooled funds from the local accounts and client wallets where the coins were stored originally and put them through tumblers and mixers, making it difficult (though not impossible) to trace the money. “Africrypt employees lost access to the back-end platforms seven days before the alleged hack,” the law firm told Bloomberg. The outlet attempted to call both Cajee brothers multiple times only to get their voicemail each time.

Complicating any recovery attempt is that South Africa’s Finance Sector Conduct Authority can’t launch a formal investigation into the incident because cryptocurrency isn’t legally considered a financial product in the country. If no one can recover the money, it will go down as the largest cryptocurrency loss in history, easily overshadowing the approximately $200 million CAD that disappeared when the founder of Canada’s QuadrigaCX exchange died while travelling in India.