Cincinnati Zoo and Botanical Garden Old Nile Hippo question about Cincinnati Zoo

[Nile Hippo Expert]

Does anyone have an exact date of death for the bull Nile Hippo "Zeeko", who was born at the Philadelphia Zoo on February 5th, 1922, and arrived at the Cincinnati Zoo on April 17th, 1924? He remained there throughout the 30s, 40s, 50s, and at least the early 60s, but he appears to have died in or before 1970.