Details emerged on Saturday of the bravery of one teacher who trapped the killer in a room, possibly preventing an even higher death toll.
"A teacher held him up and locked him into a room. He showed a lot of courage," a police spokesman said.
The teacher, Rainer Heise, told Germany's ZDF television that he had grabbed the youth's shirt and tried to talk to him.
"He then pulled off his mask and I said 'Robert?'," Heise said, calling it a Ninja-style mask.
"I said go ahead and shoot me, but look me in the face."
Steinhaeuser replied: "That's it for today," and briefly let down his guard," Heise said.
"I pushed him into the room and locked the door."
Steinhaeuser shot himself in the head shortly thereafter.

ERFURT, Germany (Reuters) - A student responsible for Germany's worst post-war massacre was a [u]gun club marksman[/u] who shot many of his 16 victims in the head at close range before an unarmed teacher stopped him, police said on Saturday.