The man, who spoke to the Herald on condition of anonymity, said Captain Zaharie was "terribly upset"when his wife told him she was leaving and believed he may have decided to take the Malaysia Airlines plane to a part of the world he had never flown in.
"He's one of the finest pilots around and I'm no medical expert, but with all that was happening in his life Zaharie was probably in no state of mind to be flying."
However, Asuad Khan, brother of Captain Zaharie's wife, spoke out in May to debunk the rumours.
"I can see that a lot of people are saying a lot of things about him which is untrue," he told ABC Australia's Four Corners programme.
Speaking on behalf of his sister, he confirmed she had not left Captain Zaharie.
Mr Khan said Captain Zaharie "had a good life".
"He had a lot of money, and he loved his daughter very much," he said.
The pilot had a flight simulator at home and had programmed flights across the Indian Ocean on the simulator. Those routes were deleted before the crash, but police were able to recover the data.
The criminal inquiry is continuing, and these initial findings have been only selectively revealed to foreign governments and air crash investigators, The Sunday Times reported.
"To date no conclusions can be made as to the contributor to the incident and it would be sub judice to say so. Nevertheless, the police are still looking into all possible angles," Malaysian police told The Sunday Times.
No sign of the plane has been found.
- Additional reporting by Lincoln Tan and Anna Leask.
