Police in South Korea have raided the airport of Muan following a deadly plane crash on site that killed almost all passengers aboard the aircraft last weekend, the Yonhap news agency reported Monday.

Authorities also raided the regional aviation office in Muan, part of Busan’s aviation administration. Read also: Black box data recovered in South Korea’s deadliest plane crash; another sent to U.S.

South Korean investigators said Saturday they were close to finalising the transcript of the cockpit voice recorder from a fatal plane crash that left 179 people dead last week.

South Korean officials are struggling to determine what caused a deadly plane crash that killed nearly 180 people on board, with the nation saddened, shocked and ashamed over the country’s worst aviation disaster in decades.

A Jeju Air passenger jet carrying 181 people from Bangkok sped off the runway and burst into flames. Two crew were rescued in what was the country’s worst air disaster in decades.

The deadliest accident in aviation history occurred in 1977, when two Boeing 747 jumbo jets collided on a foggy runway on the Spanish island of Tenerife, killing 583 of the 644 people on board the planes. Spanish investigators blamed the captain of the KLM 747 for taking off without clearance from air traffic controllers.