KUALA LUMPUR, Malaysia (CNN) -- The investigation into what happened to Malaysia Airlines Flight 370 is charging ahead on two fronts: new high-tech tools and old-fashioned police work.
While searchers scanned the ocean surface for a 26th day Wednesday with planes and ships, the possibility that something sinister may have happened hasn't been discounted.
Malaysian police said Wednesday they have interviewed about 170 people, and will continue questioning families and those who had access to the plane.
Officials have always said they were looking at four possibilities: hijacking, sabotage, personal problems and psychological issues.
A Malaysian government source told CNN on Monday that the airliner's turn off course is being considered a "criminal act," either by one of the pilots or someone else.
But a senior Malaysian government official told CNN last week that authorities have found nothing in days of investigating the two pilots that leads them to any motive, be it political, suicidal or extremist.
On Wednesday, CNN learned that Malaysia Airlines pilots have received a handout on increased cockpit security, according to two sources familiar with the airlines' operations.
The measures include a rule saying no pilot or first officer will be allowed to sit alone in the cockpit. If one or the other leaves the cockpit, a senior cabin steward must remain inside the cockpit until the pilot or first officer returns.
"These changes are positive in nature and directly relate to the MH 370 incident," one of the sources told CNN.
The flight simulator in the pilot's house is still inconclusive, police said Wednesday. Authorities are awaiting an expert's report.
"It's one of the great mysteries of our time," Australian Prime Minister Tony Abbott said in a radio interview from Perth, where he'll host his Malaysian counterpart Najib Razak later Wednesday.
"We owe it to the world, we owe it to those families to do whatever we reasonably can do get to the bottom of this."
Closed-door meeting
The plane disappeared while flying from Kuala Lumpur, Malaysia, to Beijing on March 8. Of the 239 people on board, 154 of them were Chinese nationals.
On Wednesday, families of 18 Chinese passengers met for three hours behind closed doors with Malaysian government officials and investigators in Kuala Lumpur. It's a meeting they'd been looking forward to, having accused Malaysia of not being upfront with them about the investigation.
"I personally believe today's meeting had some progress, but the time was short and family members didn't have an opportunity to raise questions," said Jiang Hui, the families' designated representative.
Jiang said the families saw new data and PowerPoint slides that hadn't been shared before -- but the flight tracks were not provided.
Malaysian authorities came under a fresh wave of criticism this week after acknowledging that the last voice transmission from the cockpit was not "All right, good night," as previously claimed, but rather "Good night Malaysian three-seven-zero."
While the difference in language may seem innocuous, the fact that authorities gave one version and let it stand uncorrected for weeks undermines confidence in the investigation, air accident investigation experts told CNN.
"High criticism is in order at this point," said Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation.
"We had a very good meeting with them," Azharuddin Abdul Rahman, head of Malaysia's civil aviation department, said after the information session with the families. "We answered all their questions."
Search zone shifts
On Wednesday, up to 10 planes and nine ships searched a swath spanning 221,000 square kilometers (85,300 square miles) northwest of Perth, Australia.
The search zone shifted eastward toward the Australian coast from where it was the day before, the Australian Maritime Safety Authority said. While this means new territory will be covered, officials caution against expecting an imminent breakthrough.
"They are looking in a vast area in very deep waters ... and we really have no idea where it went in," said Bill Schofield, an Australian scientist who helped create flight data recorders that could be key in determining what happened.
"A needle in a haystack would be much easier to find."
The plane disappeared over the waters between Malaysia and Vietnam, after signing off with Malaysian controllers but before checking in with their counterparts in Vietnam.
Authorities don't know what happened on board after that, but radar and satellite data show the plane turned off course and flew back across Malaysia and turned south over the Indian Ocean.
Based on sophisticated analysis of satellite data, investigators believe it went down in the southern Indian Ocean, but they can't pinpoint a location.
More help coming
More assets are streaming in to aid in the search, including high-tech gadgets.
The HMS Tireless, a British nuclear submarine, will take part. It'll be joined by an Australian ship with a pinger locator designed to listen for locator beacons attached to the plane's flight data recorder, plus a submersible that can canvass the ocean floor for wreckage. Both pieces of technology come from the U.S. Navy.
But there's a catch: the equipment won't be of any use until searchers are able to find wreckage from the plane to help narrow the search zone. That's because neither the pinger locator nor the submersible can quickly scan the enormous area being searched.
Under the best of sea conditions, the pingers can be heard 2 nautical miles away. But high seas, background noise, wreckage or silt can all make pingers harder to detect.
It will take the ship, the Ocean Shield, at least another day just to get to the search zone, leaving precious little time to locate the flight data recorders before the batteries on its locator beacon run out.
Time is running out: The batteries are designed to last 30 days.
There's no guarantee it will be found anytime soon. For all the expertise and technology, there's still more unknown about Flight 370 than is known about it -- including its altitude, precise speed and, especially, its final resting place.
Holly Yan reported and wrote from Atlanta; Judy Kwon reported from Kuala Lumpur; CNN's Sara Sidner, Shimon Prokupecz, David Fitzpatrick, Barbara Starr, Will Ripley, Greg Botelho, Richard Quest, Nic Robertson, Mitra Mobasherat, Kyung Lah and Yuli Yang also contributed to this report.
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