The Sampoong department store in Seoul, South Korea, collapses on this day in 1995, killing more than 500 people. The tragedy in the upscale store occurred due to a series of errors made by the designers and contractors who built the store and the criminal negligence of the store’s owner.

Lee Joon built Sampoong on the site of a former rubbish dump in 1989. It was designed to have five floors but, in the middle of construction, Joon insisted that an extra floor with a swimming pool be added. Several engineers working on the project warned Joon that this change was dangerous but, rather than taking their advice, Joon fired them. Furthermore, Seoul’s official planning department was not advised of the change and government safety inspectors monitoring the construction project were bribed, not only to cover up the design changes, but also to overlook the fact that Joon’s contractors were not using enough steel rods for support and were using an inferior grade of concrete to save money. Twelve inspectors were later convicted of accepting bribes.

By 1995, the store was very successful, with about 40,000 customers passing through its doors every day. On June 27, a gas leak was reported, but Joon refused to shut down the store. Two days later, the fifth-floor ceiling showed signs of imminent collapse. However, the only preventive measure taken was to move expensive merchandise out of the way. Some executives were also allowed to leave early.

At about 6 p.m., hundreds of people were eating dinner in the food area of the store’s basement level when the entire structure collapsed on top of them. The fifth-floor ceiling fell in and caused all the floors underneath it to buckle as well. Fires broke out throughout the structure, some fueled by gasoline from the cars parked in the store’s garage. The fires were not put out for several days.

Rescue efforts continued for weeks and, amazingly, one survivor was pulled out 16 days after the collapse. Most people were not so lucky–more than 500 died and another 900 suffered severe injuries. Twenty-five people were put on trial for charges relating to the disaster. Lee Joon was convicted of criminal negligence and received a seven-and-a-half-year prison sentence.