SEPANG, Malaysia — The search for Flight 370 turned into a criminal investigation on Saturday, after Malaysia declared that the plane had been deliberately diverted and then flown for as long as seven hours toward an unknown point far from its scheduled route from Kuala Lumpur to Beijing.
Prime Minister Najib Razak of Malaysia said on Saturday afternoon that he would seek the help of governments across a large swath of Asia in the search for the plane, which has been missing for a week and had 239 people on board. The Malaysian authorities released a map showing that the last satellite signal received from the plane had been sent from a point somewhere along one of two arcs spanning large distances across Asia.
As part of the investigation, police officers on Saturday were seen going to the gated residential compound in Kuala Lumpur where the flight’s pilot, Zaharie Ahmad Shah, was reported to live, and the Malaysian news media reported that a search there was actually underway after a week of rumors to that effect. A police spokeswoman declined to comment, saying no details would be available until a news conference planned for Sunday evening.
A satellite orbiting 22,250 miles over the middle of the Indian Ocean received the transmission that, based on the angle from which the plane sent it, came from somewhere along one of the two arcs.
One arc runs from the southern border of Kazakhstan in Central Asia to northern Thailand, passing over some hot spots of global insurgency and highly militarized areas. The other arc runs from near Jakarta to the Indian Ocean, roughly 1,000 miles off the west coast of Australia.
The plane changed course after it took off. “These movements are consistent with deliberate action by someone on the plane,” Mr. Najib said.
He noted that one communications system had been disabled as the plane flew out over the northeast coast of Malaysia. A second system, a transponder aboard the craft, abruptly stopped broadcasting its location, altitude, speed and other information at 1:21 a.m., while the plane was a third of the way across the Gulf of Thailand from Malaysia to Vietnam.
Military radar data subsequently showed that the plane turned and flew west across northern Malaysia before arcing out over the wide northern end of the Strait of Malacca, headed at cruising altitude for the Indian Ocean.
The flight had been scheduled to land at 6:30 a.m. in Beijing, so when its last signal was received, at 8:11 a.m., Mr. Najib said, it could have been nearly out of fuel.
“The investigation team is making further calculations, which will indicate how far the aircraft may have flown after the last point of contact,” Mr. Najib said, reading a statement in English. “Due to the type of satellite data, we are unable to confirm the precise location of the plane when it last made contact with a satellite.” The northern arc Mr. Najib described passes near some of the world’s most volatile countries that are home to insurgent groups, but also over areas with a strong military presence and robust air defense networks, some run by the U.S. military. The arc passes close to northern Iran, through Afghanistan and northern Pakistan, and through northern India and the Himalayas and Myanmar. An aircraft flying on that arc would have to pass through air defense networks in India and Pakistan, whose mutual border is heavily militarized, as well as through Afghanistan, where the United States and other NATO countries have operated air bases for more than a decade.
Air bases near that arc include Bagram Airfield in Afghanistan, where the U.S. Air Force’s 455th Air Expeditionary Wing is based, and a large Indian air base, Hindon Air Force Station.
The southern arc, from Indonesia to the southern Indian Ocean, travels over open water with few islands. If the aircraft took that path, it may have passed near Australia’s Cocos (Keeling) Islands. These remote islands, with a population of fewer than 1,000 people, have a small airport. After Mr. Najib’s statement Saturday, the Chinese Ministry of Foreign Affairs demanded to know more, and said that China was sending technical experts to Malaysia.
The disappearance of the jet bound for Beijing has mesmerized many in China, partly because 227 of the 239 people aboard were Chinese citizens.
The Malaysian government has said that analyzing this data is a slow and painstaking process.
David Learmount, operations and safety editor for Flightglobal, a news and data service for the aviation sector, said that the Malaysian government could have acted far sooner on the information pointing to someone seizing control of the plane.
The Indian Ocean, the third-largest in the world, has an average depth of more than 12,000 feet, or more than two miles.
Mikael Robertsson, a co-founder of Flightradar24, a global aviation tracking service, said the way the plane’s communications had been shut down pointed to the involvement of someone with considerable aviation expertise and knowledge of the air route, possibly a crew member, willing or unwilling.
The Boeing’s transponder was switched off just as the plane passed from Malaysian to Vietnamese air traffic control space, thus making it more likely that the plane’s absence from communications would not arouse attention, Mr. Robertsson said by telephone from Sweden.
“Always when you fly, you are in contact with air traffic control in some country,” he said. “Instead of contacting the Vietnam air traffic control, the transponder signal was turned off, so I think the timing of turning off the signal just after you have left Malaysian air traffic control indicates someone did this on purpose, and he found the perfect moment when he wasn’t in control by Malaysia or Vietnam. He was like in no-man’s country.”
The signs thus indicated involvement of the crew, Mr. Robertsson said, but he stressed that those signs were not definitive, nor did they prove whether any involvement was willing or coerced.
Xu Ke, a former commercial pilot who has advised the Chinese government on aviation security, said the details suggested that at least one crew member, most likely one of the pilots, was involved in seizing control of the aircraft, either willingly or under coercion.
“The timing of turning off the transponder suggests that this involved someone with knowledge of how to avoid air traffic control without attracting attention,” Mr. Xu said in a telephone interview. “You needed to know this plane, and you also needed to know this route.”
Especially since 9/11, Mr. Xu said, security on cockpit doors has been reinforced so that forced entry would be difficult without the pilots’ having ample time to send a warning signal.
“We have to be careful about our words and conclusions, and examine all the possibilities, but the likelihood that a pilot was involved appears very likely,” said Mr. Xu. “The Boeing 777 is a relatively new and big plane, so it wouldn’t be anyone who could do this, not even someone who has flown smaller passenger planes, even smaller Boeings.” The possible northern corridor Mr. Najib described bristles with military radar, making it more likely that the plane either went south or, if it did fly north, did not make it far, Mr. Robertsson said.
“I don’t really think that the aircraft could have flown so far over the land, because it would need to pass over so many countries that someone should have picked it up,” Mr. Robertsson said. “If they had taken the northern corridor, they could have gone down before they reached land, so it’s also possible.”
Huang Huikang, China’s ambassador to Malaysia, sat impassively in a light gray suit in the front row of Mr. Najib’s news conference, at an airport hotel here on the outskirts of Kuala Lumpur.
And on the website of China’s ministry of foreign affairs was a statement from a spokesman that read, “We ask that the Malaysian side provide even more comprehensive and accurate information,” the spokesman Qin Gang said.
“We urge that, based on the new circumstances, Malaysia further expand and clarify the scope of the search and intensify search efforts, and we ask that Malaysia call on even more countries to become involved in the search.
On Saturday, the announcement from Malaysia brought dismay in Beijing among family members and friends of the many Chinese nationals who were onboard the missing plane. For a week, the families and friends have gathered at a hotel, receiving updates from Malaysia Airlines employees and waiting for news. Several managed to find some relief in the announcement that at least one person had apparently seized control of the plane, because that still left a faint hope that the passengers were somehow alive somewhere.
One middle-aged man said the families would stick together until there was a definitive conclusion about the plane’s final location and fate. “We will march in the streets if we have to,” he said.
On Saturday, James Wood, the brother of Philip Wood, an American passenger on the flight said it was hard to hear that the search for the flight had turned into a criminal investigation.
“Obviously, it’s tough to deal with,” he said. “At the same time, we’re just like any other human being — we’re made of intellect and emotion. We’re trying to fight those two battles at the same time: hope and hurt.”
“Maybe they are still alive,” he added. “We have a lot of hope for that.”
It has been difficult to wait for more than a week for answers about what happened to the flight, he said.
“It’s going so slow,” he said of the investigation. “The days sometimes drag by, and we’re trying to turn off the TV because it’s just a little too hard to handle on a constant basis.”
But the family is still holding out hope for the slim possibility that he is alive.
“We have to. We just have to,” he said. “Especially when we have so many governments with so much technology looking from every direction. If they still haven’t found something, then what does that say? It leaves a lot of unanswered questions.”
According to a person who has been briefed on the progress of the investigation, the two “corridors” were derived from calculations by engineers from the satellite communications company Inmarsat, which were provided to investigators. The person spoke on condition of anonymity because details of the search operation remain confidential.
The satellite communications box fitted on the plane is of an older generation and is not equipped with a global positioning system, the person said. But investigators have managed to calculate the distance between the “ping” from the plane and a stationary Inmarsat-3 satellite orbiting above the Equator and over the Indian Ocean. The satellite can “see” in an arc that stretches to the north and south of its fixed position, but without GPS it can only say how far away the ping is, not where it is coming from, the person said.
“Imagine a torch beam coming from a satellite going left and right,” the person said, referring to a flashlight beam. “It is the maximum arc in the two directions that is being calculated.”
But based on what is already known about the flight’s trajectory, investigators are strongly favoring the southern corridor as the likely flight path, the person said. Mr. Najib’s news conference came a day after American officials and others familiar with the investigation said Flight 370 had experienced significant changes in altitude after it lost contact with ground control, and altered its course more than once as if still under the command of a pilot.