Indonesian investigators believe they have found a device containing flight data from Lion Air Flight JT610, a discovery that should help explain why the new Boeing 737 crashed Monday, killing all 189 people on board.

CNN Indonesia showed images of divers retrieving the device, which houses flight data, commonly known as a "black box."

Video showed the device being brought on board one of the rescue ships in the sea off Jakarta Thursday, four days after the Boeing 737 MAX 8 jet disappeared off radar during a routine short-haul flight.

On Thursday the National Transportation Safety Committee (NTSC) head Soejanto Tjahjono confirmed to CNN that one of the aircraft's two black boxes has been recovered, but could not confirm which one.

There are two parts to a black box -- a cockpit voice recorder (CVR) which records audio from the cockpit, and a flight data recorder (FDR). They're both housed in the tail of the aircraft.

Tjahjono said it was "likely" that the device found was the FDR.

He said it will take two to three weeks to read the data, and a further two to three months to analyze it. He added that "some parts" of the plane's fuselage has been found.

Monday's ill-fated flight crashed 13 minutes after takeoff. It was supposed to be a one-hour flight to Pangkal Pinang on the island of Bangka.

Capt. Daniel Putut Kuncoro Adi, managing director of Lion Group, which owns Lion Air as well as other airlines, told CNN that "as a company we are waiting for the result from the NTSC working with the black box" to determine what went wrong with Monday's flight.

He said that he knew the pilots on the flight and they "were very funny, very smart, very nice guys. We believe the pilots did their job professionally and they struggled to save the aircraft." He also offered his condolences to the families of the victims. (CNN)