NEW YORK — New York City’s celebrity owl Flaco died from a traumatic impact, zoologists confirmed a day after he reportedly flew into a building, with further testing planned to determine if the Eurasian eagle-owl may have been sick.

What happened in Flaco’s final hours is top of mind for his fans across the city, who cheered him on as he defied the odds by fending for himself despite a life in captivity. Police are still seeking to arrest whoever let him out of his enclosure at the Central Park Zoo a year ago.

Flaco had been in good physical shape, the necropsy found, succeeding in catching prey even though he had no experience hunting because he came to the zoo as a fledgling 13 years earlier. According to the necropsy report released Saturday, the owl weighed 1.89 kilograms (4.1 pounds), just 2% less than when he was last measured at the zoo.

Flaco was found dead Friday on a sidewalk after apparently hitting a building on Manhattan’s Upper West Side.

“The main impact appears to have been to the body, as there was substantial hemorrhage under the sternum and in the back of the body cavity around the liver,” the report said.

The Central Park Zoo put the blame squarely on the person who cut open Flaco’s enclosure. But they’re investigating illness as a possible factor, and plan to release an update in around two weeks.

“This will include microscopic examination of tissue samples; toxicology tests to evaluate potential exposures to rodenticides or other toxins; and testing for infectious diseases such as West Nile Virus and Avian Influenza,” the zoo’s statement said.

Eulogies from his admirers poured in over the weekend. So did speculation about which of the many urban threats to wildlife may have contributed to his death.

Flaco fans who listened for his nightly hooting in on the Upper West Side reported he’d gone quiet in the days before his death, and theorized that he may have been ill.