Practically every shooting is used as an excuse to call for knee-jerk "MOAR GUNS KONTROL!!!lll111" as opposed to actually, you know, enforcing the laws meant to keep guns out of irresponsible and unstable hands that we already have.
The supposed twitter account was created in 2011. The shooter is 18. A bit of math says it was created when the shooter was 7.
The twitter account probably does not belong to the shooter.