Of course his trans identity is important. There have been a number of school shootings in the US over recent years where the shooter identified as trans.
To understand the problem, to put in place interventions to try to prevent this, the authorities need to know 'why'. Yes being male is a factor, but its only part of the picture. Some of the other school shooters were female.
So why is this happening. Are people with significant mental health problems attracted to gender ideology. Does it help them, does it make their problems worse. Conversely does adopting a trans identity lead to the development or exacerbation of mental health problems. Do cross sex hormones have a role to play. What about social isolation (though Minneapolis is a very trans positive state and his parents appear to have been affirming)
I could go on but you get the picture.