Leyda Cuellar (plaintiff) and Richard Joyce (defendant) were married and had a daughter, K.C., in Panama. Joyce took K.C. to the United States without Cuellar’s knowledge. Cuellar filed a petition under the Hague Convention on the Civil Aspects of International Child Abduction (Convention) to have K.C. returned to Panama. Joyce argued that a return would harm K.C. Specifically, Joyce stated that: (1) Cuellar was poor and lived in a Panamanian slum with no running water, (2) K.C. exhibited symptoms of ataxia and other neurological conditions and needed to stay in the United States for treatment, and (3) K.C. had become attached to her new home and would suffer psychological harm from a return to Panama. In support of his medical claims, Joyce testified that an unidentified physician had diagnosed K.C., but Joyce did not call the physician as a witness. In addition, Joyce admitted that he did not know what medical treatment was available in Panama. The district court found that there would be a grave risk of harm to K.C. if she were returned to Panama. The district court denied Cuellar’s petition. Cuellar appealed.