Police on Tuesday questioned a doctor from a Seoul university hospital as part of an investigation into the deaths of four premature babies from bacterial infection in December.

Cho Su-jin, who was in charge of Ewha Womans University Medical Center's intensive care unit for newborns, faced an interrogation over whether she neglected her duty to supervise her staff to ensure the proper treatment of the babies, according to police.

"I am sorry," Cho told reporters as she entered the police station.

Cho refused to answer questions from the police, officials said. Just two hours after the interrogation began, she returned home due to health problems, they said.

"We plan to call her in again," a police official said, declining to be named.

Cho's legal representative told reporters that she has been suffering from cancer and depression.

Last week, police said that the Dec. 16 deaths of the newborns were caused by blood poisoning from a bacterial infection.

Blood tests on the infants showed that all of them were infected with Citrobacter freundii, which can cause fatal symptoms in immunocompromised patients, including premature babies, police said, citing the autopsy results from the National Forensic Service. (Yonhap)