Police are focusing on finding out when and why a gas-fired boiler disconnected from an exhaust pipe, leading to the deaths of three students of carbon monoxide poisoning at a guesthouse in Gangneung.

Police have tentatively concluded the three died of carbon monoxide poisoning as exhaust gas leaked through a gap between the boiler and the pipe. The other seven in the group have been hospitalized and are slowly recovering.

They are looking into when and why the boiler and pipe were disjoined, and who is responsible for safety management of the boiler system at the guesthouse.

Having sent the boiler to the National Forensic Service, police are questioning the guesthouse owner, the company that installed the boiler, the gas supplier and previous guests of Room 201 where the accident took place.

The guesthouse owner has told the police that groups of Koreans and foreign visitors had stayed at the room earlier this month, and that the room was empty for about 10 days before the 10 students from Seoul’s Daesung High School occupied it.

An official of the investigation team said they are also working to identify fingerprints on the pipe.

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