"A powerful detonation in Moscow". Putin's trusted dead

According to the news agency TASS, an detonation occurred on Monday morning in the lobby of the luxury residential complex “Skarłatne Żagle” at Lotnicza Street in the northwestern part of the capital of Russia. According to the media, 2 people died and 3 were injured. Among the killed is the founder fighting against Ukraine of the Armenian battalion “Arbat”. At the entrance to the building, a homemade explosive device would explode. The men were accompanied by bodyguards. Who's Armen Sarkisjan? He is formally the head of the Bokser Union of the alleged Donetsk People's Republic, and unofficially the Armenian-origin politician who formed the Collaborate Battalion ‘Arbat’. What's the formation?