Israel’s Shin Bet has held Russian-Israeli historian Artem Kirpichenok for more than a month without disclosing why. His family says the case may involve espionage.

Historian and writer Artem Kirpichenok flew to Tel Aviv on August 2 to attend an international conference, his support group said. Officers from Israel’s General Security Service (Shin Bet) detained him at the airport. Kirpichenok, a citizen of both Russia and Israel, has remained in custody ever since. Officials have not disclosed the reason for his detention.