Sunny, a 19-month-old female red panda, went missing from the Virginia Zoo on Jan. 24, 2017

| Credit: The Virginia Zoo/Twitter

The Virginia Zoo in Norfolk is not giving up hope in finding Sunny, the red panda who went missing over three-and-a-half years ago.

In a new interview with The Virginian-Pilot, zoo director Greg Bockheim said that Sunny's disappearance remains the "greatest mystery" of his career.

On the morning of Jan. 24, 2017, Sunny, a 19-month-old female red panda, went missing from her exhibit at the zoo. The Norfolk Police Department joined in the initial search, using geothermal cameras to scour the zoo grounds.

But nearly four years later, Sunny is still at large.

Bockheim told The Virginian-Pilot that he lies awake at night wondering "where she could have gone, what could have happened to her. I just hope she’s out there somehow and doing well."

Due to the lack of evidence that Sunny was abducted, Bockheim said he believes that Sunny slipped off a wet tree branch extending over the fence line.

Bockheim also said that given Sunny's friendly personality, he is worried she still hasn't been found. "She would have been seen by now," he said. "She was not afraid of people. She was friendly."

"I don’t see how you could keep that quiet," Bockheim added of the possibility of someone coming across Sunny. "Friends. Neighbors. Someone would notice a red panda in a cage in your house. They’d report it."

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Rob Vernon, a spokesperson for the Association of Zoos & Aquariums, told The Virginian-Pilot that zoo escapes are typically rare, occurring only about half a dozen times per year.

"I can tell you, in most cases, the animals who do leave their habitat never leave zoo grounds," Vernon told the newspaper. "In fact, most 'escapes' involve animals accessing keeper service areas rather than animals completely outside of their habitat and at risk of coming into contact with the public, though it does occasionally happen."

Sunny's Twitter account, which is run by a "random person," according to Bockheim, is still in use, though infrequently.

"I'm still here waiting to be found," the account tweeted on Sunday.

On Jan. 24, the account wrote, "Today is my 3-year escape anniversary. Does anyone still think about me? It’s very lonely out on the streets all by myself #FindSunny."

Anyone with information on Sunny should call the zoo's hotline at 757-777-7899.