Pilot Zaharie Ahmed Shah is being held solely responsible for veering flight MH370 off course, according to one investigator.
Speaking to USA Today, the unnamed official said Shah 'deliberately' redirected the plane. He was the only one who had the experience and expertise to fly the plane and there was no evidence of a mechanical failure or a passenger hijack attempt.
It comes as his estranged wife Faizah Khan and other family members are quizzed this week to help shed light on his state of mind in the lead-up to the plane's disappearance on 8 March.
The official, who is not authorised to talk publicly regarding the probe, said investigators believe Shah had no links to militant groups and his co-pilot Fariq Abdul Hamid was not experienced enough to pull off such a diversion.
He also said nothing in Shah's finances suggested anything was amiss and denied reports that Shah received a mystery call from a woman moments before the Beijing-bound flight took off.
He said as far as the team knew, a phone call to his mobile was not received at that time.
The MH370 took a sharp westward turn off-course an hour after take-off from Kuala Lumpur and headed towards the southern Indian Ocean.
The international search operation, now in its third week, was halted by bad weather on Wednesday following a 'credible' sighting of '122 floating objects'.
None of the objects, however, has been confirmed to have being directly linked to the missing jetliner.
Malaysian investigators had come under mounting pressure from the FBI to interview Shah's wife Khan, who was given time to grieve for her husband following the jet's disappearance.
One source said: "The whole world is looking for this missing plane and the person who arguably knows most about the state of mind of the man who captained the plane is being left alone."
Shah was also known to be a 'fanatical supporter' of Anwar Ibrahim's People's Justice Party, the opposition party which has been the principal thorn in the side of the United Malays National Organization (UMNO), which has ruled Malaysia for 56 years.
Shah's flight left the day that Ibrahim was sentenced to five years in prison on sex crimes - his supporters say the charges are fraudulent.