A day care staff member suspected of suffocating an infant to death was found to have repeatedly abused seven other infants, prosecutors said Wednesday.

The investigation team on crimes against women and children at the Seoul Southern District Prosecutors’ Office said it has detained and indicted the 59-year-old suspect surnamed Kim on charges of child abuse.

Prosecutors also indicted without detention Kim’s twin sister who runs the child care center in Hwagok-dong, western Seoul, and another staff member, 46, for abetting Kim’s crimes.

Around noon on July 18, Kim allegedly wrapped a blanket around an 11-month-old boy, clasped his body tight for about six minutes, and sat on him for eight seconds, suffocating him to death.

As the infant was healthy and seen playing as usual at the child care center that morning, prosecutors believe there to be no other reason behind his death.

Prosecutors found that Kim had smothered a total of eight infants by rolling a blanket around their bodies and clasping them tightly with her arms on 24 occasions last month.

“Covering an infant’s face with a blanket repeatedly exposes the infant to a lack of oxygen, and can damage brain cells and affect development, therefore constitutes an act of abuse,” the prosecution said.

Kim also did not comply with the basic safety education manual for child care staff.

According to the manual, the care workers must lay infants less than 12 months old on their backs to prevent sudden death from suffocation, and not make the room dark in order to keep check on the infants.

Kim told prosecutors she had been putting the infants to sleep by covering them with a blanket to keep them from moving, so she could rest.

In addition to abetting Kim’s acts of abuse, her twin sister -- the center’s director -- and another staff member often mistreated the infants by pushing them. The director frequently left the center during work hours to go to the gym or other places.

Prosecutors also found that the director made false reports to the authorities to receive government subsidies.

She received a total of 100 million won ($88,200) in government subsidies from September 2013 to July this year by allegedly lying that her sister and the other staff member worked eight hours per day.

The ward office of Gangseo-gu is set to shut down the child care center, suspend the three suspects’ qualification as day care workers for two years and retrieve the subsidies.

Qualification as a day care worker is revoked for those sentenced to jail for child abuse.

“Ward offices and child protection agencies need to check security cameras more often,” said a prosecutor on the case. “The prosecution and police are providing financial support and counseling for the victim’s family.”

The Gangseo Police Station, which conducted the initial investigation of the case, is looking into the center’s closed-circuit TV footage from January to June.

By Kim So-hyun (sophie@heraldcorp.com)