(CNN) -- As investigators search for clues to unravel the mystery of where Malaysia Airlines Flight 370 went, there were several key developments over the weekend.
But major questions still remain.
Here's a cheat sheet to help you get up to speed on the latest developments:
Where are investigators searching now?
The search has expanded to cover large swaths of land and sea, including 11 countries and deep oceans. Where the plane went is anybody's guess. As 25 nations help try to find where the missing plane is, there's also a process of elimination in which investigators try to piece together where the aircraft isn't. Pakistan said Sunday that the plane never showed up on its civilian radars and would have been treated as a threat if it had. The Times of India reported that India's military also said there was no way the plane could have flown over India without being picked up on radar.
What's one main focus of the investigation?
Malaysia's Prime Minister has said that somebody deliberately steered the plane off course. That means the pilots have become one obvious focus for investigators. On Sunday, Malaysian police said they were still investigating a flight simulator seized from pilot Zaharie Ahmad Shah's home. Peter Chong, a friend of the 53-year-old pilot, said it's unfair to imply Zaharie had anything to do with what happened to the plane. He told CNN he'd been to Zaharie's house and tried out the flight simulator. "It's a reflection of his love for people," Chong said, "because he wants to share the joy of flying with his friends."
A 29-year-old Malaysian civil aviation engineer, Mohammed Khairul Amri Selamat, who works for a private jet charter company was on the flight. Police are investigating all passengers and crew, but he is likely to be of particular interest because of his aviation knowledge. "I am confident that he is not involved," his father told CNN. "They're welcome to investigate me and my family."
What do we know about key moments on the flight?
For days we've been talking about the last transponder signal the plane sent. And now it appears another system that sends data about the plane, the Aircraft Communications Addressing and Reporting System (ACARS) was shut off, too. Authorities say that system was disabled early on in the flight, just before the plane flew over the east coast of the Malay Peninsula. Before the transponder was deactivated, the co-pilot is believed to have made the plane's last verbal communication with air traffic controllers. "All right, good night." (1:19 a.m.). At 2:40 a.m., military radar spotted the plane hundreds of miles off course. And at 8:11 a.m. -- more than seven hours after takeoff -- a satellite tracked the plane as it attempted a series of "handshakes" -- or electronic connections -- with it.
While some details have come into focus, major questions remain unanswered:
Where's the plane?
Satellite and radar data have given authorities some clues, but not enough to pinpoint the plane. Right now investigators are focusing on two corridors where the plane might have either crashed or landed: a northern arc that stretches from the border of Kazakhstan and Turkmenistan in central Asia to northern Thailand, and a southern arc that spans from Indonesia to the southern Indian Ocean. Because the northern parts of the traffic corridor include some tightly guarded airspace over India, Pakistan and even some U.S. installations in Afghanistan, U.S. authorities believe it's more likely the aircraft crashed into waters outside of the reach of radar south of India, a U.S. official told CNN. If it had flown farther north, it's likely it would have been detected by radar.
Who would deliberately divert it?
In addition to the pilots, other passengers and crew members onboard the plane, as well as any ground staff who came into contact with it, are under investigation. The bottom line, investigators say, is that whoever flew the plane off course for hours appeared to know what they were doing. Investigators are looking into the backgrounds of the passengers to see whether any of them were trained pilots. "There are still a few countries who have yet to respond to our request for a background check," said Khalid Abu Bakar, inspector general of the Royal Malaysian Police Force. "But there are a few ... foreign intelligence agencies who have cleared all the(ir) passengers." According to The New York Times, one of the passengers was an aviation engineer on his way to Beijing to work for a private-jet company.
Why would they do it, and how?
Finding a motive behind the plane's disappearance is a key problem investigators must solve. So far, they haven't released any concrete details. Speculation has surgedabout the possibility of terrorism or hijacking, but that hasn't been confirmed.
Is there any chance the passengers and crew survived?
It's possible the plane's last satellite contact could have been made from the ground, as long as the airplane still had electrical power, Malaysia's civil aviation chief Azharuddin Abdul Rahman said Sunday. For the families and loved ones of those aboard Flight 370, some find comfort that there's no evidence the plane crashed. The father of one passenger, who watched updates from Malaysia in a Beijing hotel, said he hoped the plane was hijacked because that gave him reason to think his son had survived. "I hope they are alive," he said, "no matter how small the chance is."
Does the possibility that the plane is on land change anything about the investigation?
Yes, analysts told CNN. It means it's even more pressing that authorities find the plane. "Time is even more of the essence. If this airplane has been taken to be used as a weapon, then the time that has been taken to prepare the aircraft for whatever deed is the plan -- obviously to thwart that, it's all about time," said Shawn Pruchnicki, who teaches aviation safety and accident investigation at Ohio State University. CNN aviation analyst Jim Tilmon, a former American Airlines pilot, said whoever deliberately steered the plane off course likely did it with help. But what's next is anyone's guess, he said. "We have been behind them all along," he said. "So now, if they had a plan, and if that plan included being able to set down someplace and refuel a little bit, we are looking at something that we may never see the end of."
CNN's Samira Jafari and Ram Ramgopal contributed to this report.