Virgil Griffith, 36, who lives in Singapore and works for the blockchain and cryptocurrency developer Ethereum, was arrested at Los Angeles International Airport on Thursday, the Justice Department said.

He attended a conference on blockchain and virtual currencies in Pyongyang in April, where he spoke about how to use both technologies “to evade sanctions,” the department said.

Doing so violated US Treasury bans on “exporting any goods, services, or technology” to North Korea, put in place in response to the country’s nuclear weapons program.

“Despite that the US Department of State had denied Griffith permission to travel to the DPRK (Democratic People’s Republic of Korea), Griffith presented at the DPRK Cryptocurrency Conference, knowing that doing so violated sanctions against the DPRK,” the Justice Department said in a statement.

The department said North Korean officials at the conference appeared to show particular interest in Griffith’s presentation.

After the conference, it said, Griffith “began formulating plans to facilitate the exchange of cryptocurrency between the DPRK and South Korea, despite knowing that assisting with such an exchange would violate sanctions.”

The Justice Department said he also announced plans to renounce his US citizenship, aiming to “purchase” citizenship in another country.

“We cannot allow anyone to evade sanctions, because the consequences of North Korea obtaining funding, technology, and information to further its desire to build nuclear weapons put the world at risk,” said FBI Assistant Director William Sweeney.

Called a “cult hacker” in a New York Times profile 11 years ago, Griffiths has a doctorate in theoretical neuroscience from California Institute of Technology.

Three years ago he joined Ethereum, a Singapore-based company developing a secure blockchain-based global platform for business and finance use, and promoting its own cryptocurrency of the same name.