"In the beginning, both babies were doing well, but in the course of Wednesday, we had observed that one was becoming weaker," Frankfurt Zoo director Manfred Niekisch says in the Frankfurter Neue Presse.
Niekisch explains that the zoo is allowing Dian, aged 26, to carry the dead infant around with her rather than force her to give officials the baby, according to translated news reports.
"We are letting nature take its course," says Niekisch.
Niekisch also adds that zoo officials are reluctant to take the baby from Dian because she could react in a way that might harm the surviving child. And if she is given a sedative, the drug could compromise her breast milk.