Chinese officials have said the incident on March 7 involved a foiled assault by passengers, but they have revealed few details. The aircraft was on its way from the restive, mostly Muslim region of Xinjiang to Beijing when it cut short its journey and landed in Lanzhou, a city in the north-west.
The Communist Party chief of Xinjiang, Wang Lequan, said this week that the incident was a failed attack by separatists based abroad seeking an independent Xinjiang.
One source with direct knowledge of the official Chinese inquiry has said the chief suspects - a man and a woman - boarded the flight as Pakistani nationals.
"The woman was carrying flammable liquids and evaded security checks by going through the first-class boarding area," said the source, an expert on Xinjiang security threats who has spoken to investigators. The source declined to be identified because of the risk of punishment for revealing sensitive information.
"They were carrying Pakistani passports," the source said.
"That does not mean they've concluded they were Pakistani nationals. The passports may have been fake or illegally obtained."
But the source also said the woman had been born in Xinjiang and spent many years in Pakistan.
An aviation industry source said the woman was a young Uighur trained by a Pakistan militant group, and the man was from Central Asia and in his 30s.
A third suspect, a Pakistani, who masterminded the bungled attack, was at large, the aviation industry source said.
The suspects boarded the aircraft with two canned drinks, the content of which had been replaced with a flammable liquid using a syringe, the second source said. The woman failed to light the liquid in the aircraft toilet, the source said. She aroused the suspicion of crew and other passengers when she came out of the toilet to pick up the second can.
The Chinese Foreign Ministry had no immediate comment.