I wonder if he is suffering from schizophrenia (obviously not treated IMO) as was reported,
whether somebody sitting close to him
(a seat right in front of him)
triggered some psychotic/delusional/paranoid attack.
(He was seen observing the victim before stabbing)
Other passengers were some distance from the perp.
I'm just trying to understand what caused the attack.
If he was aggressive at home
(mother forced him to leave)
I don't understand why the perp wasn't forcefully put into a mental hospital for treatment
An insane man was on the loose.
Anybody could be attacked.
He could be hearing voices, etc., telling him to kill.
He could also treat others as threats in this sick mind.
All this is horrific
RIP Iryna

Sincerest Condolences to Family.
JMO