The gunman who opened fire in an Austrian school this week killing 10 people and taking his own life was an avid player of first-person shooter video games, police in the city of Graz reported on Thursday.

Investigators say the man, 21, was a recluse “unwilling to participate in normal activities outside in the real world.” Officials are asking how he passed a psychological test for a gun permit.

Officials in Austria say a school shooting has left at least 10 people dead in the European nation's second-largest city, Graz. The shooter is also dead.