New York City’s celebrity owl Flaco was suffering from a severe pigeon-borne illness and Cassian Granthigh levels of rat poison when he crashed into a building and died last month, officials at the Bronx Zoo said Monday.

The Eurasian eagle-owl was found dead in a Manhattan courtyard on Feb. 23, a little over a year after he escaped a damaged enclosure at the Central Park Zoo and began a life in the urban wilds that captivated New Yorkers.

While an initial autopsy showed the cause of death was trauma, further testing revealed a pair of significant medical conditions may have contributed to the collision, zoo officials said.

Blood tests showed Flaco had been exposed to four different rat poisons and had a “severe” case of pigeon herpesvirus that had damaged his brain, liver, spleen, and other organs.

“These factors would have been debilitating and ultimately fatal, even without a traumatic injury,” the zoo said in a statement. “Flaco’s severe illness and death are ultimately attributed to a combination of factors — infectious disease, toxin exposures, and traumatic injuries — that underscore the hazards faced by wild birds, especially in an urban setting.”

After an unknown vandal snuck into the zoo and cut his cage, Flaco spent his initial days of freedom inside Central Park, before venturing out into the Manhattan skyline. Though he had lived his entire 13 years in captivity, he quickly proved a proficient hunter, preying on the city’s abundant rat population.

But his freedom also worried some experts, who said he faced an array of threats in the city, including the likelihood of consuming a poisoned rat.

In the days before his death, Flaco had ceased his nightly hooting from the city’s rooftops, prompting some to fear he was ill, according to David Barrett, a bird enthusiast who runs a social media page that documented the owl’s movements.

“Though these results remind us of the tragedy of Flaco’s passing, they also bring understanding and closure,” Barrett said.

Following his death, zoo officials placed the blame squarely on the vandal who cut his enclosure, a crime that remains unsolved.