Klaus managed to break into the Necropolis at Telemok and steal a Necklace of Fireballs from Cosmo Phobas' tomb with the help of a group of other bandits. The other bandits were killed by Damon, but Klaus managed to get away by throwing all of the fireballs from the necklace.
He might have escaped the Necropolis, but because the tomb was consecrated, Klaus received the Curse of the Graverobber. Thus he was in the process of slowly dying when he tried to pass the curse off to the Oracle's Chosen in Estoria.
He was unsuccessful and moved on to try and get rid of the curse in Mytros instead: and it is assumed that he died on the way there.