City officials say they believe that their finance director was suffering from brain damage caused by a rare parasite that he picked up while traveling in Mexico a few years ago. The damage impairs a person's social decision-making abilities.

The city was not aware of Keogh's illness until Wednesday, when Keogh's wife, Karlene, informed them that the parasite had affected his brain and other parts of his body.

The family said it believes the accident "is related to the impacts of this disease on his central nervous system," City Manager Frank Fairbanks said.

Scottsdale police had not determined late Thursday whether Keogh's death was accidental or intentional. But police said Keogh, 55, climbed out the driver's window of his Mercedes-Benz and stood atop the moving vehicle, arms outstretched.