Nur-Ab-Sal owned a necklace into which he transferred his spirit upon death. The necklace was one of the artifacts found in the Jastro Expedition, which Sophia Hapgood kept for herself. Sophia was never separated from the necklace and she claimed it guided her. When she was reunited with Indiana Jones, he suspected it had some kind of negative effect on her.
When they reached Atlantis, Nur-Ab-Sal's spirit took over her, but Indy got rid of the necklace, freeing Sophia from its control.