. Were other people involved?
. or other organisations such as extremists organisations?
. Did he have people egging him on (even if totally uninvolved otherwise), or was he a complete loner?
. Is there a hidden motive here that's not obvious?
. Further evidence of stable and rational thinking, or mentally unstable?
. Is it possible he was aided by legal loopholes, or some failures in process that need patching?
. Could he have left any nasty surprises behind?
. Does his behaviour indicate something that would allow prediction of similar crimes and perhaps their thwarting?
. Photos/films of something of interest like supporters, discussions of further action, whatever
In this case, once a crime is committed, all info needs to be gathered. I'm saying that as someone who is disturbed at extensions of state powers, but once there's a crime, I'm all for picking up everything and analysing it.