The announcement was widely expected and has broad support in the country: A recent poll showed that about three-quarters of all Finns support joining the military alliance.
Prosecutor General Iryna Venediktova says 21-year-old Vadim Shishimarin shot and killed an unarmed man while fleeing from Ukrainian defense forces. He's in custody and could face life in prison.
The final battle for Mariupol is taking place inside the Azovstal steel plant, a massive coastal complex in the besieged city. Hundreds of civilians are still trapped inside, officials say.
Ukrainian and international experts believe it will take years, if not decades, to build cases and prosecute people. Ukraine's prosecutor general's office has opened more than 9,000 investigations.