The last words from a Malaysian passenger jet missing for 10 days were apparently spoken by the co-pilot, the airline says, providing a glimpse into the crucial period when the plane was deliberately diverted.

Clarification that the voice was most likely that of First Officer Fariq Abdul Hamid came during a press conference at which Malaysian officials hit back at “irresponsible” suggestions that they had misled the public – and passenger’s relatives – over what happened to Malaysia Airlines Flight 370.

Captain Zaharie Ahmad Shah and his co-pilot Fariq Abdul Hamid have become a primary focus of the investigation, with one of the key questions being who was in control of the aircraft when it veered off course about an hour into its flight to Beijing.

The nonchalant-sounding last message from the cockpit – “All right, good night” – came around the time that two of the plane’s crucial signalling systems were manually disabled.

“Initial investigations indicate it was the co-pilot who basically spoke,” said Malaysia Airlines CEO Ahmad Jauhari Yahya.

The last signal from the Aircraft Communications Addressing and Reporting System (ACARS) was received 12 minutes before the co-pilot’s final words.

The plane’s transponder – which relays the plane’s location – was switched off just two minutes after he spoke, and a few minutes later the aircraft turned back on its flight path.

Yahya said it was not clear precisely when the ACARS system, which sends a signal every 30 minutes, was disabled. Officials had previously maintained it was manually turned off before the final cockpit message.

The Malaysian authorities have stressed that the backgrounds of all the passengers and crew were being checked, as well as engineers who may have worked on the plane before take-off.

But Michael McCaul, chair of the US House Homeland Security Committee, said US intelligence briefings had seemed to lead “towards the cockpit, with the pilot himself, and co-pilot”.

The plane went missing early on March 8 with 239 passengers and crew aboard, spawning a massive international search across Southeast Asia and the Indian Ocean that has turned up no trace of wreckage.

AFP