I'd say that Gerald Cotten's scam of USD 190 million when he "died" in India, the exchange of which he was CEO said he was the only one with the passwords.

Sorry for the cancer site: https://economictimes.indiatimes.com/small-biz/startups/newsbuzz/crypto-exchange-ceo-dies-in-india-platform-cant-pay-investors-as-he-had-the-passwords/articleshow/67861832.cms