Two brothers in South Africa have disappeared along with $3.6 billion worth of bitcoin that was housed on their cryptocurrency investment platform, according to a Cape Town law firm hired by investors to investigate the alleged heist.

The law firm, Hanekom Attorneys, said it has reported the incident to the Hawks, an elite unit of South Africa’s national police force. Hanekom has also reported the matter to South African financial regulators and crypto exchanges around the world.

The brothers, Ameer and Raees Cajee, set up their crypto investment service, Africrypt, in 2019.