Did Jet Try to Avoid Radar?

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:

Report: Plane flew low to avoid radar

Whoever was flying the airplane may have flown below 5,000 feet and used mountainous terrain as cover to avoid being detected by radar, the New Straits Times newspaper in Malaysia reported Monday, citing unnamed sources. CNN could not immediately confirm the newspaper's account, which is just one of several as-yet unproven theories about what happened to the jetliner after its last contact with flight controllers.

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 26 nations help try to find the missing plane, 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's, said it's unfair to imply that Zaharie had anything to do with what happened to the plane. He said 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 said. "They're welcome to investigate me and my family."

See full story as it changes at CNN.com.