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.
The perpetrator thinks he is smarter than police, has a level of training in such matters. 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.
I think he is going to get caught. I think there will be an arrest within 3 months.
#supposition
AIMOO