CNN — KUALA LUMPUR, Malaysia (CNN) -- Absent any explanation supported by evidence for what may have happened to Malaysia Airlines Flight 370, the inspector general of Malaysian police said Wednesday that authorities were redoubling their efforts -- but he pleaded for patience.
"We have to clear every little thing," Khalid Abu Bakar told reporters after a speech at a police academy here. "You cannot hurry us in whatever we are doing."
Among the things included in "every little thing" is an investigation into the people who prepared the food for the flight, he said. "That also we'll have to look into," he said.
Progress, of a sort, has been made, in that investigators have cleared all 227 passengers of any role in hijacking or sabotage and of having personal or psychological issues that might have played a role in the plane's disappearance, he said.
And a senior Malaysian government official told CNN last week that authorities have found nothing about either of the pilots to suggest a possible motive.
No such comments have been made about the rest of the crew of 12.
The investigation into what may have caused the plane to appear to vanish on March 8 on a flight from Kuala Lumpur to Beijing has been a criminal one since March 16, the inspector general said.
That corroborates a report from a Malaysian government source who told CNN on Monday that the airliner's turn off course -- either by one of the pilots or by someone else -- was considered a "criminal act."
"It's ongoing; we have not concluded the whole thing, and we are still awaiting for expertise reports from experts overseas and internally," Khalid said.
Meanwhile, the exhaustive search for clues continued. Malaysian police said earlier Wednesday they had interviewed about 170 people and were planning to continue questioning relatives of the 239 people who were aboard the Boeing 777-200ER, as well as others who may have had access to the plane.
Police have said they were looking at four criminal possibilities: hijacking, sabotage, personal problems and psychological issues.
Mechanical failure has not been ruled out either.
Malaysia Airlines pilots have received a handout on increased cockpit security, two sources familiar with the airline's operations told CNN on Wednesday.
The measures include a rule saying no pilot or first officer is allowed to sit alone in the cockpit. If one or the other leaves the cockpit, a senior cabin steward must be inside the cockpit until the pilot or first officer returns.
"These changes are positive in nature and directly relate to the MH370 incident," one of the sources told CNN.
"What they put in place is pretty common sense," said Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation. "That's been the rule in the United States for at least a decade."
An investigation into a flight simulator found in the pilot's house is inconclusive, police said Wednesday. Authorities were 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.
"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."
Private meeting with families
Of those aboard, 154 were Chinese nationals.
On Wednesday, families of 18 Chinese passengers met privately for three hours with Malaysian government officials and investigators in Kuala Lumpur. The meeting had been called after they accused Malaysia of not being up-front with them about the investigation.
"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."
The families' representative saw it differently. "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.
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 said this week that the last voice transmission from the cockpit was not "All right, good night," as they had previously said, but "Good night Malaysian three-seven-zero."
While the difference may appear inconsequential, the fact that authorities gave an incorrect version and let it stand for weeks undermines the public's confidence in the investigation, air accident investigation experts told CNN.
"High criticism is in order at this point," said Schiavo.
Malaysian Prime Minister Najib Razak was to arrive late Wednesday in Perth, Australia, and travel north to the Royal Australian Air Force's Pearce Air Base for a briefing and to meet Thursday with search personnel. He is also scheduled to meet with Abbott, his Australian counterpart.
Search zone shifts
On Wednesday, up to 10 planes and nine ships searched 85,300 square miles (221,000 square kilometers) of ocean northwest of Perth.
The search zone shifted eastward toward the Australian coast from where it had been on Tuesday, the Australian Maritime Safety Authority said.
"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 the flight data recorders that, if found, could prove key to the investigation.
"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, flew back across Malaysia and turned south over the Indian Ocean.
Based on analysis of satellite data, investigators believe it went down in the southern Indian Ocean, but they can't pinpoint where.
More help coming
More assets are streaming in to aid in the search, including high-tech gadgets.
The HMS Tireless, a British nuclear submarine with sonar capabilities, will take part. It will be joined by an Australian navy ship equipped with a pinger locator designed to listen for locator beacons attached to the plane's flight data recorder, plus a submersible that can search the ocean floor for wreckage.
But the equipment won't be of use until wreckage from the plane is found and the search zone narrowed. That's because neither the pinger locator nor the submersible -- both of which are from the U.S. Navy -- can quickly scan the enormous area being searched.
Under the best of sea conditions, the pingers can be heard 2 nautical miles away. That distance shrinks in the presence of high seas, background noise, wreckage or silt.
It will take the Austalian navy ship, the Ocean Shield, at least another day to reach the search zone, leaving little time to locate the flight data recorders before the batteries die on its locator beacon.
Time is running out: The batteries are designed to last 30 days -- until April 7.
There's no guarantee the plane will be found soon -- or ever. Though the Boeing jetliner was among the world's most sophisticated planes, much about Flight 370 remains unknown -- including its altitude, precise speed and, especially, its final resting place.