The dead man had given evidence in a 2017 murder case in Ukraine in which a man who had plotted to murder Russian President Vladimir Putin was injured and his wife killed in a gun attack near Kiev, the Ukrainian interior ministry told AFP.
Austrian police have arrested a Russian from Chechnya over the fatal shooting of a Chechen dissident, officials said on Sunday.
A 43-year-old was found dead with gunshot wounds near the capital Vienna on Saturday, police said in a statement.
They arrested a 47-year-old in the city of Linz, some 200 kilometers (125 miles) from Vienna, adding: «The motives for the crime are unclear.»
The Austrian police said the dead Chechen was an asylum seeker but declined to comment further.
A prosecution spokesman identified the dead man as Chechen government critic Martin B., adding prosecutors were seeking a court order to keep the suspect in detention.
The suspect lives in Austria but is originally from the Chechnya region.
The Austria shooting comes amid growing concern over the security of Chechen dissidents living in exile.
In February, an exiled Chechen blogger also critical of Chechen leader Ramzan Kadyrov fended off an attacker armed with a hammer.
A month earlier, Chechen opposition leader Imran Aliev was found dead in a hotel room in the northern French city of Lille, stabbed 135 times.
Chechnya is a predominantly Muslim Russian republic in the North Caucasus. Two wars in the 1990s triggered a wave of emigration, with many Chechens heading for western Europe.
More Chechens have fled into exile in recent years because of disagreements with pro-Kremlin Kadyrov, who rights activists accuse of repeated rights violations.