Given that a northern route would have sent the plane over countries with busy airspace, most experts say the person in control of the aircraft would more likely have chosen to go south. The southern Indian Ocean is the world's third-deepest and one of the most remote stretches of water in the world, with little radar coverage.
Whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience, putting one or both of the pilots high on the list of possible suspects, Malaysian officials and aviation experts said.
Zaharie, the captain, was a supporter of a Malaysian opposition political party that is locked in a bitter dispute with the government, according to postings on his Facebook page and a friend, Peter Chong, who is a party member.
Chong said that he last saw Zaharie a week before the pilot left on the flight for Beijing and that they had agreed to meet on his return to organize a shopping trip for poor children.
"If I am on a flight, I would choose Captain Zaharie," he said. "He is dedicated to his job. He is a professional and he loves flying."