The Korean National Police Agency’s National Office of Investigation said Monday that they are investigating 939 cases of what are popularly being referred to as “ghost children” in an ongoing nationwide probe to discover unregistered babies.

So far, police have confirmed that 34 of the unregistered babies have died. Investigators are looking into the possibility of 11 babies having been killed by their own parents, according to local reports quoting police. Nineteen other cases were closed after being cleared of suspicions, they explained.

Of the total cases police are looking into, the whereabouts of 782 babies remain unknown, while only 146 babies have been located.

Police said they had received a total of 1,069 reports of undocumented newborns as of late Friday afternoon. The highest number of cases were filed with the Seoul Metropolitan Police, with 205 reports, while only five cases were filed to Sejong City Police, they added.

Seoul Gwanak Police Station is looking into two suspicious deaths and found that the newborns had died at the hospital after receiving medical care immediately following birth in 2015 and 2016. Gyeonggi Nambu Provincial Police, Busan Metropolitan Police and Incheon Metropolitan Police are each investigating one death case.

As of Monday, four infanticide cases have been referred to the prosecution after police found evidence possibly indicating their parents’ involvement in the deaths of their children.

South Korea launched a wide-scale nationwide probe late last month to identify the whereabouts of 2,123 undocumented babies born since 2015 and verify whether they are alive or dead. Local authorities have faced difficulties tracking those born before 2014 due to poor data management.

Investigation results are set to be announced Wednesday at the earliest.