Investigators probing the MH370 mystery today said they cannot rule out the possibility it was hijacked as they released a 400-page report into the disappearance of the doomed flight.
Officials said the plane, which went missing en route from Kuala Lumpur to Beijing in March 2014 with 239 on board had diverted from its flight path manually rather than due to a mechanical fault while 'interference by a third party' could not be excluded.
But angry families of those on board remain without definitive answers to one of aviation's greatest mysteries after experts said they are still unable to say why exactly the Boeing 777 disappeared.
Years of investigations have found no firm evidence as to what happened to the Malaysia Airlines plane.
This morning, families of missing passengers said the Malaysian government's final report on the aircraft had no new findings and officials said they were 'unable to determine the real reason for the disappearance'.
But while finding the plane was airworthy and the pilots were in a fit state to fly, the report did highlight mistakes and protocols and guidelines that were not followed, the families told reporters after a briefing on the report.
Lead investigator Kok Soo Chon said this morning that the probe had confirmed the plane had turned back under manual control and that 'we cannot exclude the possibility that there was unlawful interference by a third party.'
He said this morning: 'We can conclude that MH370 had turned back and the turn back was not because of anomalies in the mechanical system. The turn back was made not under autopilot but under manual control.'
However, the team was unable to say why exactly the plane had strayed off its path and disappeared.
Kok said: 'We cannot determine with any certainty the reason the plane diverted from its planned route. The team is unable to determine the real reason for the disappearance.'
'The answer can only be conclusive if the wreckage is found,' he said when asked of they would ever find out what happened on the plane.
The report reiterated Malaysia's assertion that the plane was deliberately diverted and flown for more than seven hours after severing communications.
Relatives who were briefed at the transport ministry before the report's public release expressed anger that there was nothing new in the document, with some storming out of the briefing as frustration boiled over.
'It is so disappointing,' said Intan Maizura Othman, whose husband was a steward on MH370. 'I am frustrated. There is nothing new in the report.
'Those who gave the briefing from the ministry of transport were not able to give answers as they were not (the ones) who wrote the report.'
She said the meeting between relatives and officials descended into a 'shouting match' as family members' frustration boiled over.
'Many asked questions,' said G. Subramaniam, who lost a son on the flight, but added that 'unsatisfactory responses left many angry'.
One area that came in for criticism in the report by the 19-member investigation team, which included foreign investigators, was air traffic control.
It said both Malaysian air traffic control and their Vietnamese counterparts failed to act properly when the Boeing jet passed from Malaysian to Vietnamese airspace and disappeared from radars.
Air traffic controllers did not initiate emergency procedures in a timely fashion, delaying the start of the search and rescue operation, it said.
However it played down concerns about the pilot and first officer, saying neither appeared to have suffered difficulties in their personal lives that could have affected their ability to fly.
It also said the plane was airworthy and did not have major technical issues. This however meant that the plane's change of course 'was likely made while the aircraft was under manual control and not the autopilot', the report said.
Intervention by a third party could not be ruled out, it said, but also added there was no evidence to suggest the plane was flown by anyone other than the pilots.
The report also dismissed one conspiracy theory about the plane's disappearance - that it was taken over remotely to foil a hijacking, saying there was no evidence to support this.
Experts believe someone may have deliberately switched off MH370's transponder before diverting it over the Indian Ocean.
The last communication from the plane was from the Captain Zaharie Ahmad Shah who signed off with 'Good night, Malaysian three seven zero', as the plane left the Malaysian airspace.
A 440-page final report by the Australian Transport Safety Bureau (ATSB) last year showed that Zaharie had flown a route on his home flight simulator six weeks earlier that was 'initially similar' to the one actually taken by MH370.
A forensic report by the Malaysian police previously concluded that there were no unusual activities other than game-related flight simulations.
Kok said the investigators examined the history of the pilot and the first officer, and they were satisfied with their background and training and mental health.
'We are not of the opinion it could have been an event committed by the pilots,' he said, but added they were not ruling out any possibility since the in-air turn back was done manually and the systems in the plane were also manually turned off.
'We cannot exclude that there was an unlawful interference by a third party,' Kok said.
He added all the passengers of the 15 countries had their backgrounds checked by their respective countries and all came back with a clean bill of health.
Voice 370, a group representing the relatives, has previously urged the Malaysian government for a review of the flight, including 'any possible falsification or elimination of records related to MH370 and its maintenance'.
The families said the report pointed to mistakes by the Malaysian air traffic control (ATC) centre. It showed there were only two attempted phone calls made to the aircraft from the ground, four to five hours apart.
The Malaysian Minister of Transport Anthony Loke had earlier said the report would be released on Monday after families of those on board were briefed.
'Every word recorded by the investigation team will be tabled in this report,' he said.
'It will be tabled fully, without any editing, additions or redactions.'
More than four years after the aircraft vanished on March 8, 2014, investigators have had little luck in finding the wreckage of the plane that vanished with 227 passengers on-board, plus the captain, co-pilot and 10 crew.
Only three confirmed fragments of MH370 have been found, all of them on western Indian Ocean shores, including a two-metre wing part known as a flaperon.
Malaysia's new government, which took power in May, has said the hunt could be resumed but only if new evidence comes to light and officials have seemed keen to draw under a line the tragedy.
Captain Shah, who was going through a marriage breakup, is believed to have downed the aircraft in an act of murder-suicide, by diverting from the flight path and plunging into the Indian Ocean, off the coast of Western Australia.
The four-year search for MH370 ended in May after the US-based technology firm Ocean Infinity failed to locate the plane while canvassing 125,000sq/km of the Indian Ocean.
Malaysia had signed a 'no find, no fee' deal with Ocean Infinity to resume the hunt for the plane after the official search led by Australia, Malaysia and China was called off in early 2017.
Several theories have emerged about how the plane disappeared, with some suggesting the plane was hijacked and others believing someone on board may have deliberately turned off the plane's transponder before diverting it over the Indian Ocean.