The captain of missing Malaysia Airlines flight MH370 received a two-minute call shortly before take-off from a mystery woman using a mobile phone number obtained under a false identity, as investigators question the pilot's estranged wife, a British newspaper reported.
It was one of the last calls made to or from the mobile phone of Captain Zaharie Ahmad Shah in the hours before his Boeing 777 left Kuala Lumpur on March 8, reported The Mail on Sunday.
Investigators are treating it as potentially significant because anyone buying a pay-as-you-go SIM card in Malaysia has to fill out a form giving their identity card or passport number.
Introduced as an anti-terrorism measure following 9/11, this ensures that every number is registered to a traceable person.
But in this case police traced the number to a shop selling SIM cards in Kuala Lumpur. They found that it had been bought 'very recently' by someone who gave a woman's name - but was using a false identity.
The discovery raises fears of a possible link between Captain Zaharie, 53, and terror groups whose members routinely use untraceable SIM cards. Everyone else who spoke to the pilot on his phone in the hours before the flight took off has already been interviewed.
In a separate development, The Mail on Sunday has learned that investigators are now poised to question Mr Zaharie's estranged wife in detail.
They have waited two weeks out of respect, but will now begin formally interviewing Faizah Khan following pressure from FBI agents assisting the inquiry.
Although the couple - who have three children - were separated, they had been living under the same roof.
A source said: 'Faizah has been spoken to gently by officers but she has not been questioned in detail to establish her husband's behaviour and state of mind in the days leading to the incident.
The mystery caller emerged when Malaysian investigators examined the phone records of both Mr Zaharie and his co-pilot, 27-year-old Fariq Abdul Hamid. Investigators were keen to trace the caller and interview them, although they have stressed that the fact that the SIM card was registered to a non-existent ID card does not necessarily indicate a criminal or terrorist connection.