In reality, Hengist was possessed by a non-corporeal lifeform named Redjac, known as Jack the Ripper on Earth. It fed on the fear of its victims, and it was responsible for the murders. While it was inhabiting Hengist's body, the administrator tried to discourage attempts by the crew of the USS Enterprise to investigate the murder of Kara, saying on one occasion, "This is purely an Argelian matter." The evidence that ultimately pointed to his harboring the murderous entity was the murder weapon itself, a knife produced by the Hill People of Rigel IV.
Upon this fact being revealed, Redjac killed Hengist, and attempted to enter the Enterprise. It was unsuccessful, so it re-entered Hengist, re-animating the administrator's body. Hengist's body, with the lifeform in it, was beamed out into space in a wide dispersal pattern, killing the lifeform. (TOS: "Wolf in the Fold")