Almost certain people going to the concert are not all that responsible for what their president is doing. They are partially if they didn’t vote or tired to stop him, but little effect that would have. Innocent victims, are innocent. No matter the country they live in.
What I am finding extremely annoying is that Russia was warned about this, and they dismissed it as propaganda or whatever shithead in charge dismissed it as. Now that it came to happen they think they have the right to demand anything.