South Korea — Three people were found dead inside a car in a joint suicide, police said Monday, following a similar incident a day earlier.

Officials said they discovered a van, with three dead people inside, that was parked in front of a rest area on a road in Injae, Gangwon Province, at around 9 a.m.

The van contained two males and one female who appear to have died from inhaling toxic fumes from burning charcoal briquettes inside the car, authorities said. The time of their deaths was not known. The woman, identified only by her surname Lee, was found in possession of a suicide note.

Investigators suspect that the three met and communicated through the Internet to plan their collective suicide, as they had no apparent personal ties and lived in different parts of the country.

The incident added shock after two other group suicides in the province over the past week.

On Thursday, six people were found dead together in a rented lodging facility in Hoengseong County, while two others were discovered dead last week in the county of Jeongseon, all in what are presumed to be suicides planned through the Internet. Both also involved the use of charcoal briquettes.