The search for missing Malaysia Air Flight 370 may become a lot more complicated, if a new theory by American investigators turns out to be true. At first, the assumption was that the flight ended when the transponders stopped communicating; then military radar suggested the plane may have turned back and reached the other side of the Malaysian peninsula. Now data from engine transmissions to maintenance databases suggest the plane remained in operation for four hours after its last confirmed transmission — which makes the potential search range all but endless:

U.S. investigators suspect that Malaysia Airlines3786.KU -4.08% Flight 370 stayed in the air for about four hours past the time it reached its last confirmed location, according to two people familiar with the details, raising the possibility that the plane could have flown on for hundreds of additional miles under conditions that remain murky.

Aviation investigators and national security officials believe the plane flew for a total of five hours, based on data automatically downloaded and sent to the ground from the BoeingCo. BA -0.99% 777’s engines as part of a routine maintenance and monitoring program.

That raises a host of new questions and possibilities about what happened aboard the widebody jet carrying 239 people, which vanished from civilian air-traffic control radar over the weekend, about one hour into a flight to Beijing from Kuala Lumpur. …

But the huge uncertainty about where the plane was headed, and why it apparently continued flying so long without working transponders, has raised theories among investigators that the aircraft may have been commandeered for a reason that appears unclear to U.S. authorities. Some of those theories have been laid out to national security officials and senior personnel from various U.S. agencies, according to one person familiar with the matter.

Malaysian officials dispute this version of events:

Malaysia’s government categorically denied a report on Thursday suggesting a missing passenger jet flew on for four hours after vanishing from air traffic control systems, as the search entered a sixth day and speculation and theories about the plane’s fate continued to mount.

The problem with the denial is that Malaysian officials have very little credibility left in this crisis:

Malaysian authorities have faced mounting criticism about their transparency and their handling of the case, and they struggled Wednesday to say why they were only now revealing the military data. A day earlier, Malaysian military officials gave a series of conflicting statements about whether the plane had indeed tacked west.

Malaysia’s military said it noticed the recorded data only after the fact, not in real time. …

China, which had 153 passengers on board, has been the most vocal critic of Malaysia’s response, and an editorial Wednesday in the state-run Global Times asked whether the Malaysian military “was hiding anything on purpose.”

“We hope Malaysia can face its own shortcomings, and cooperate with China with a more open and candid attitude,” the editorial said.

China hasn’t done much better. The satellite images seen yesterday of potential debris turned out to be days old, and of poor quality. Ships in that area report seeing nothing of what was seen in the photos, but thanks to the delays, the debris spotted might have sunk or drifted far off with the currents. The photos were not announced publicly, but simply posted to a website where no one took notice of them for several hours.

If the plane flew another four hours, it could have made it as far as India or Australia. The Wall Street Journal mapped the new search area that would be in effect under those circumstances:

It’s the equivalent of looking for a needle in the world’s biggest haystack. On the other hand, it includes plenty of potential landing sites, so perhaps there may be a few more unexpected turns in this story.