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.

Investigators of the Jeju Air crash are close to completing the conversion of the cockpit voice recorder from audio to text in the hope it may provide more clues as to what caused the aviation disaster.