A large-scale police search is underway for a family of three that went mysteriously missing on a remote island last month.

Ten-year-old Cho Yu-na and her parents in their 30s went missing in Wando, South Jeolla Province, from May 31 after they entered the island in a silver-colored Audi sedan two days earlier.

The family stayed at a guesthouse near a beach on the island after arriving, but cell phone signals of Cho and her mother were last found at a location near the guesthouse at around 1 a.m. on May 31, and the signal for Cho’s father was gone at 4 a.m. near a harbor on the island.

The vehicle never left the island, according to surveillance camera footage obtained by investigators. The family was last seen leaving the guesthouse at around 11 p.m. on May 30 from surveillance camera footage.

The police search started on June 22 after officials with the elementary school in Gwangju that Cho attended filed reports to law enforcement upon seeing the mailbox of her home filled with unopened mail.

Cho reported to the school that she will be on a family trip for a month to Jeju Island from May 19 to June 15, the school told the police. However, Cho failed to report to school after the announced travel period, which prompted school officials to visit her home in Gwangju.

Wando was reported to have a home for Cho’s relatives at one point, but no one was found to be residing there around the time of the incident, police told media. The family was also found to have never entered Jeju Island as opposed to Cho’s report made to the school.

The police suspect the family could have fallen into the sea while inside the vehicle, hinting the three might have committed suicide. Cho’s father was known to be in financial troubles after closing a business and being unemployed.

Around 100 officials are taking part in the search, but they have not found any additional signs of the vehicle or the three family members thus far.