By NATHANIEL POPPER and REBECCA R. RUIZ
The American and European authorities said on Thursday that they had shut down two of the largest online black markets, AlphaBay and Hansa Market, and arrested their operators.
AlphaBay, the largest so-called dark net market, was taken down in early July at the same time the authorities arrested the reported founder of the site, Alexandre Cazes, a Canadian man who was living in Bangkok.
Mr. Cazes committed suicide in his jail cell shortly after he was arrested, the authorities said on Thursday. He was 25 years old.
After AlphaBay went down, users streamed to one of its largest competitors, Hansa Market.
But on Thursday, the Dutch national police announced that they had taken control of Hansa Market in June and had been operating the site since then, monitoring the vendors and customers and gathering identifying details on those involved in the 50,000 transactions that took place.
Two men were arrested in Germany in June and accused of operating Hansa Market.
When dark net markets are shut, their users typically move quickly to new markets. But on Thursday, news of the joint operation sent the community into a panic.
“DO NOT MAKE NEW ORDERS ON ANY DNM ANY MORE!” a popular post on the social network Reddit said on Thursday, using initials for dark net markets.
“You got this one law enforcement,” the post said.
AlphaBay and Hansa Market were successors to the first and most famous market operating on the so-called dark net, Silk Road, which the authorities took down in October 2013.