Austrian police have arrested a leading opponent of Kazakh President Nursultan Nazarbayev on suspicion of murder.
Lawyers for Rakhat Aliyev say he flew to Vienna voluntarily for questioning by Austrian investigators.
Mr Aliyev, a former son-in-law of Mr Nazarbayev, is wanted in Kazakhstan over the murder of two bankers, kidnapped in 2007 and later found dead.
Austria has twice refused to extradite him. He used to be Kazakh ambassador to Vienna. He denies the charges.
Mr Aliyev, who currently lives in Malta, fell out with the Kazakh president in 2007 and says the Kazakh accusations against him are politically motivated.
A businessman with wide contacts among the Kazakh elite, he spoke out against Mr Nazarbayev after being sacked as ambassador.
Austria has refused to extradite him because of concerns about human rights in the ex-Soviet Central Asian republic.
He was formerly married to Dariga Nazarbayeva, eldest daughter of Mr Nazarbayev, an authoritarian ruler who has cracked down hard on any dissent.
Austria opened its own investigation into Mr Aliyev in 2011.