BEIJING — Like an Agatha Christie whodunit, the investigation of the disappearance of Malaysia Airlines Flight 370 is now focusing on a finite circle of suspects: the 227 passengers and 12 crew members of the missing plane.While loath to call it a hijacking, Malaysian officials say they believe someone on the plane with expertise in the navigational and communications systems of the Boeing 777 diverted it from its Kuala Lumpur-to-Beijing flight path.“In view of this latest development, Malaysian authorities have refocused their investigation into the crew and passengers on board,” Malaysian Prime Minister Najib Razak said at a news conference Saturday. But, he said, “despite media reports that the plane was hijacked, I wish to be very clear we are still investigating all possibilities for what led … Flight 370 to deviate from its flight path.”‘Failed hijacking’?U.S. investigators renewed their background checks on the passengers and crew Saturday.They have turned up no evidence of any “traditional” Islamic terrorist link to the plane’s disappearance. But they remain intrigued about who might have diverted the jumbo jet westward from its planned course.“This is feeling like kind of a failed hijacking,” a federal law enforcement official said anonymously.The official said U.S. authorities theorized that once the plane was diverted toward the Indian Ocean, it was flown erratically at high altitudes in an attempt to depressurize the cabin and render the passengers unconscious. “That could have neutralized any threat from them to take the plane back,” he said.