Dutch prosecutors accused Russia on Monday of allowing a suspect in the downing of flight MH17 to return to rebel-held eastern Ukraine in defiance of an extradition agreement.
Vladimir Tsemakh, an alleged air defence specialist for pro-Moscow separatists, was one of dozens of prisoners exchanged by Kiev and Moscow in September in a deal hailed as a first step towards ending five years of conflict.
The Netherlands said it had then immediately asked Moscow at the highest levels to hand him over for questioning over the 2014 downing of the Malaysia Airlines plane, but that Russia said it could not find him.
"According to media reports Mr Tsemakh had already returned to his residence in eastern Ukraine," the Dutch prosecution service said in a statement.
"The Public Prosecution Service has concluded that Russia willingly allowed Mr Tsemakh to leave the Russian Federation and refused to execute the Dutch request, while under the European Convention on Extradition, it was obliged to do so."