The ACARS reporting system on the missing Malaysia Airlines Boeing 777 was taken off air prior to the pilots’ last radio contact with Malaysian ATC, Malaysian defense and transport minister Hishammuddin Hussein said.

At a press briefing in Kuala Lumpur afternoon, the minister confirmed the brief exchange “All right, good night” from MH370’s cockpit came after the ACARS [Aircraft Communications Addressing and Reporting System] communications system was disabled, but before the disappearance of the 777 from radar screens. Although it is not clear who made that call, there were unconfirmed reports Monday that it was made by the Malaysia Airlines co-pilot.

Malaysia’s Prime Minister, Najib Razak, confirmed Saturday that MH370 had its tracking transponders turned off in "what looked like a deliberate action from somebody on board the aircraft."

Najib said forensic work by aviation authorities showed there was a "high degree of certainty that the ACARS transmission was disabled just before the aircraft left the Malaysian east coast." Following that, some way between Malaysia and the Vietnamese coasts, the ATC transponder was also turned off.

At Sunday’s briefing, the defense and transport minister said that satellite data and forensics analysis has focused the investigation and search on two corridors. The first was from as far north as Kazakhstan through to Thailand, with a second corridor running from Indonesia to the South Indian Ocean, off Australia.

“We are looking at a search area covering 22 countries … over a huge area not just of sea, but land as well,” he said. The Malaysian authorities, he said, were being actively assisted by 25 countries in the search process.

As well as refocusing the investigation on background checks of “crew, passengers and ground staff”, the Malaysian police have taken possession of a flight simulator from the home of MH370 captain, Zaharie Ahmad Shah, and are examining it and analyzing the data it contains, Malaysian police chief Khalid Abu Bakar said.

A police spokesman added that the aircraft’s cargo manifest had been screened, and found to contain no hazardous goods, and that so far, no demands or communications had been received from any outside groups.

“We are now looking at one of four possible scenarios. These are sabotage, terrorism, hijacking and personal problems,” Abu Bakar said.

There were 239 people onboard the missing aircraft and there has so far been no sign of its location.