The FBI joined forces with Malaysian authorities in analysing deleted data on a flight simulator belonging to the pilot of the missing Malaysia Airlines plane, while distraught relatives of the passengers unleashed their anger - wailing in frustration at 12 days of uncertainty.
Files containing records of flight simulations were deleted on February 3 from the device found in the home of the Malaysia Airlines pilot, Captain Zaharie Ahmad Shah, Malaysian police chief Khalid Abu said.
It was not immediately clear whether investigators thought that deleting the files was unusual.
The files might hold signs of unusual flight paths that could help explain where the missing plane went. Then again, the files could have been deleted simply to clear memory for other material.
Defence Minister Hishammuddin Hussein told a news conference that Zaharie was considered innocent until proven guilty. He said members of the pilot's family are cooperating in the investigation.
Zaharie was known to some within the online world of flight simulation enthusiasts.
In a post on one forum, the CEO of flight simulation software company PMDG wrote that Zaharie was a customer who "had developed an online presence in which he dedicated many hours of his time to promoting the enjoyment of flying generally, and flight simulation specifically."
The company CEO, Robert Randazzo, could not be reached directly for comment, but the publisher of the popular forum AVSIM Online, Tom Allensworth, confirmed that the post was from Randazzo.
A US official, speaking on condition of anonymity because the official was not authorised to discuss the ongoing investigation by name, said the FBI has been asked to analyse the deleted simulator files.
In his first public comments on the mystery, President Barack Obama told a US television station that finding out what happened to the missing flight MH370 was a top US priority.
"It's a big piece of planet that we're searching and sometimes these things take time," Obama said.
He offered his thoughts and prayers to the relatives of the missing passengers.
"I want them to be assured that we consider this a top priority.
"We have put every resource that we have available at the disposal of the search process."
Obama said US agencies including the FBI and the National Transportation Safety Board was available to the investigation.
Flight 370 disappeared March 8 on a night flight from Kuala Lumpur to Beijing. Malaysian authorities have not ruled out any possible explanations, but have said the evidence so far suggests the flight was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled.
They are unsure what happened next and why.
Investigators have identified two giant arcs of territory spanning the possible positions of the plane about 7 hours after takeoff, based on its last faint signal to a satellite - an hourly "handshake" signal that continues even when communications are switched off.
The arcs stretch up as far as Kazakhstan in central Asia and down deep into the southern Indian Ocean.
Police are considering the possibility of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board, and have asked for background checks from abroad on all foreign passengers.
Hishammuddin said such checks have been received for all the foreigners except those from Ukraine and Russia - which account for three passengers. "So far, no information of significance on any passengers has been found," he said.
The 53-year-old pilot joined Malaysia Airlines in 1981 and had more than 18,000 hours of flight experience. People who knew Zaharie from his involvement in opposition political circles in Malaysia and other areas of his life have described him as sociable, humble, caring and dedicated to his job.
The crisis has exposed the lack of a failsafe way of tracking modern passenger planes on which data transmission systems and transponders - which make them visible to civilian radar - have been severed. At enormous cost, 26 countries are helping Malaysia look for the plane.
FAMILIES WAIT FOR ANSWERS
Relatives of passengers on the missing airliner - two-thirds of them from China - have grown increasingly angry over the lack of progress in the search. Planes sweeping vast expanses of the Indian Ocean and satellites peering on Central Asia have turned up no new clues.
At a hotel near the Kuala Lumpur airport, one of the Chinese women who was removed from the room displayed a banner that said, in part, "We are against the Malaysian government for hiding the truth." She later expressed frustration with officials.
"We launch our demands every day but to no answer, and they tell me to come back the next day," she said. "No answer, every day."
The father of passenger Pushpanathan Subramaniam said in an interview that the wait was "really too much."
"I don't know why it is taking so long for so many people to find the plane. It's 12 days," said 60-year-old Subaramaniam Gurusamy from his home on the outskirts of Kuala Lumpur. His 34-year-old son, Pushpanathan, was on the flight to Beijing for a work trip.
"He's the one son I have," Subaramaniam said.
Hishammuddin said a delegation of Malaysian government officials, diplomats, air force and civil aviation officials will head to Beijing - where many of the passengers' relatives are gathered - to brief the next of kin on the status of the search.
Aircraft from Australia, the US and New Zealand searched an area stretching across 305,000 square kilometres of the Indian Ocean, about 2600 kilometres southwest of Perth, on Australia's west coast. Merchant ships were also asked to look for any trace of the plane.
China has said it was reviewing radar data and deployed 21 satellites to search the northern corridor, although it is considered less likely that the plane could have taken that route without being detected by military radar systems of the countries in that region.
Indonesian Defence Minister Purnomo Yusgiantoro said Indonesia military radar didn't pick up any signs of Flight MH370 on the day the plane went missing. He said Malaysia had asked Indonesia to intensify the search in its assigned zone in the Indian Ocean west of Sumatra, but said his air force was strained in the task.
"We will do our utmost. We will do our best. But you do have to understand our limitations," Purnomo said.