The black boxes of a Boeing jetliner that crashed in South Korea last month stopped recording about four minutes before the accident, South Korean officials said Saturday, possibly complicating investigations into the cause of the disaster that killed 179 people.

Flight recorders from the passenger jet that crashed in South Korea last month, killing more than 170 people, stopped working minutes before the plane belly-landed and exploded on the runway, investigators said Saturday.

South Korean investigators previously said the flight data and cockpit voice recorders were key to finding out the cause of last month’s crash that killed 179 people