Rusty the red panda, who briefly ran free in D.C. in 2013, has unexpectedly died

In this handout provided by the Smithsonian National Zoo, a male red panda named Rusty is seen in his exhibit in the Smithsonian National Zoo in 2013 in Washington, D.C. (Handout/Getty Images)

Some who were in Washington, D.C., in 2013 are mourning the loss of Rusty the red panda, who captivated the city when he escaped from the Smithsonian's National Zoo almost a decade ago. He was 10 years old.

He died on Oct. 14. Pueblo Zoo, where he was living, currently does not know the cause of death, Sandy Morrison, marketing and communications manager at Pueblo Zoo, told NPR in an email.