GYEONGJU, North Gyeongsang Province (Yonhap) ― Police said Monday that they have begun looking into whether structural flaws were to blame for last week’s gymnasium collapse that killed 10 people, most of them college students, and injured 105 others.

The roof of the gymnasium at the Mauna Ocean Resort in Gyeongju, a historic tourist city 370 kilometers southeast of Seoul, caved in on Feb. 17 when some 560 incoming freshmen from the Busan University of Foreign Studies were holding a welcome party inside the building.

After holding a joint on-site inspection with structural engineers and studying an architectural blueprint of the building, police said that not enough bolts had been used to support the roof.

“Only two bolts were used to hold together an auxiliary pillar and the surface (of the roof), while there were four bolts on the blueprint,” a police officer close to the investigation told a press briefing.

Initially it was thought that snow that had piled up on the roof could have been a major cause of the collapse. Hit by severe winter storms, the Gyeongju area received snowfall of more than 50 centimeters around the time of the accident.

“There is a possibility that the bolt was not sufficiently fastened or that the structure could not bear the weight,” said Park Yeong-seok, a civil engineer who participated in the joint inspection. Police, however, reiterated that the exact cause of the collapse has yet to be determined as an in-depth investigation is still underway.

The structure, built as a gymnasium in 2009, used roof panels and rigid frames along with light gauge metal wall cladding. Such buildings are widely used as storage units.