Malaysian officials are backing away from assertions made during the weekend that Malaysian Airlines Flight MH370's ACARS system had been turned off before the plane's last contact with air-traffic controllers.

Officials are now saying that the last ACARS message from the plane—a Boeing 777-200ER on a scheduled flight from Kuala Lumpur to Beijing on March 8—was received at 1:07 a.m. and that the next one would have been due 30 minutes later but never arrived.

Given the newly released timeline, it's possible that ACARS was turned off before last contact with ATC at 1:19 a.m., or later, and it's also possible that all systems had been manually disabled after the last conversation with ATC.

MH370 was seen on secondary civil radar for the last time at 1:21 a.m. before the coverage became patchy, and contact was lost altogether at 1:30 a.m.

The first officer has since been identified as having made the last communication with air traffic control at 01:19 a.m. local time. “All right, good night,“ he stated when the aircraft was nearing the IGARI waypoint and was about to be handed over to the Ho-Chi-Minh-City ATC center in Vietnam.

The flight disappread from radar about 40 minutes after take-off with 239 on board.

The search and rescue effort now involves 26 countries. Two arcs have been identified as possible areas where the aircraft could have come down. They are identified by what is believed to have been the last known position over the Strait of Malacca and calculations on minimum and maximum speed.

At minimum speed for the Northern arc, the aircraft would have been over Laos and at maximum speed over the Caspian sea. For the southern arc, minimum speed would have taken the aircraft to the West of Sumatra and maximum speed way to the South of the Indian Ocean and significantly West of Australia.

According to Malaysia Airlines CEO Ahmad Jauhari Yahya, the aircraft is calculated to have had fuel for another 30 minutes flying depending on speed after the last time contact was established with an Inmarsat satellite. No data had been exchanged so the position at that time is unclear. MH370 was last detected at 8:11 a.m. local time on March 8 around 7.5 hours after take-off, apparently close to when trip fuel and reserves for the Beijing route would have been consumed.

Malaysian officials now believe someone on board had taken control of the aircraft, but there are diverging opinions about whether one of the pilots or another person should be suspected. The pilots' homes were searched over the weekend.

Malaysian Chief of Police, Khalid Abu Bakar, said “We are now looking at one of four possible scenarios. These are sabotage, terrorism, highjacking and personal problems.”

Yahya said MH370’s suspected flight plan, as reconstructed from radar and satellite data, had been flown in a 777 flight simulator. “It confirmed it was possible for it to fly that,” he said.