For now the EU has only frozen the bulk of Russian assets. The cases where assets or money has been seized are in cases such as sanctions violations. EU countries are unlikely to seize anything unless they have a solid legal justification.
It was already stolen money. Stolen from the Russian people, by crooks who support a war criminal in his imperialist massacres (the people whose assets are being frozen weren't selected randomly). These oligarchs forfeited their wealth by supporting the aggressor and threatening the countries where they stashed their loot. There is a crystal-clear justification for locking these assets for the trillions Russia will have to pay in reparations.
