Pavel Durov, the Russian-born billionaire tech entrepreneur who with his brother Nikolai Durov co-founded the encrypted messaging app Telegram and serves as its CEO, is in custody after being arrested at an airport outside of Paris, law enforcement officials in France confirmed on Monday. He could be detained through Wednesday in connection with a probe into illegal activity on Telegram. After that, he would have to be released or charged.

It’s not currently clear whether charges have been brought against Durov himself, as a press release from French prosecutors only describes his arrest as part of an ongoing “judicial investigation” of an “unnamed” individual alleged to be complicit in a range of crimes encompassing fraudulent transactions, the sale of narcotics, and possession of child sexual abuse material (CSAM). Police sources indicated that the arrest stemmed from Telegram’s lack of moderation and failure to comply with authorities looking for evidence of crimes on the platform. Durov left Russia in 2014 after refusing government demands to censor anti-Putin commentary on his social network VK (he also sold his stake in the site) and now holds dual citizenship in France and the United Arab Emirates.

Russia banned Telegram, which was popular among pro-democracy organizers, in 2018, but lifted the block in 2020 in part because users were getting around it with VPNs. One Moscow politician, Maria Butina, said that the arrest of Durov by France’s anti-fraud pol.