While the living slept, Zane was walking among the dead. Because he was what the system considered to be a "Living Dead" Zane could walk outside the safety of his temporary sanctuary without needing to fear an attack from these monsters.
Because of this, the young man entered the Main Building which was now a domain of the dead. As Zane walked past the undead monstrosities that now plagued this world, they did not pay him the slightest notice. Instead, he observed his surroundings, finding the halls stained with coagulated blood, and the bones of the victims who had been entirely devoured by the Walkers.
The hinges on the classroom doors, and the doorways to other areas had been blown off, and the doorway themselves had been irreparably damaged by some kind of significant force. Zane, of course, could guess exactly what this was. Keith had turned into a higher level of undead. One which Zane did not know yet know the name of.