AlphaBay was a successor to the first and most famous market operating on the so-called dark net, Silk Road, which the authorities took down in October 2013.
AlphaBay grew into a business with 200,000 users and 40,000 vendors — or 10 times the size of Silk Road — the Justice Department said on Thursday.
Mr. Cazes, originally from Canada, had his laptop open and was logged in to AlphaBay at the time of his arrest, allowing the authorities to gain access to all of AlphaBay’s hidden servers and financial accounts, according to legal documents unsealed on Thursday.
Mr. Cazes committed suicide in his jail cell shortly after he was arrested, the authorities said on Thursday. He was 25 years old.
The authorities have moved quickly to seize Mr. Cazes’ significant assets, including properties in Antigua, Cyprus and Thailand; 10 vehicles, including a Lamborghini and a Porsche; and financial assets of about $18 million.
Some of Mr. Cazes’ money was in the virtual currencies used on AlphaBay, including Bitcoin, Ether and Monero. He also had bank accounts in Liechtenstein, Thailand and Cyprus.
Officials said they had found Mr. Cazes because he posted his personal email address, [email protected], in some early messages from AlphaBay.
Even before AlphaBay went down, it had several large competitors. In the last few weeks, a site known as Dream Market has emerged as the leading player.
On Thursday, Dream Market had 57,000 listings for drugs and 4,000 listings for opioids.