I'm adding to my supposition, psychiatric problems.
I don't think there is a direct relationship with the victims. I think there has been contact with the person in some context, possibly online. The victims have been stalked online.
The perpetrator has had underlying internalised anger issues. I don't think he is Incel but holds some similar contempt for the victims.
The perpetrator thinks he is smarter than police, has a level of training in such matters, i.e. as stated prior, military training. There may not be enough evidence at present.
I don't think he lives in Moscow. I think he lives on his own. I think he did the crime in a timeframe that no one noticed he was gone. He would have been home in time for work, unnoticed. He's at least 220lbs.
I think he is going to get caught. I think there will be an arrest within 3 months.
#supposition
AIMOO