Story highlights

Many experts believe the plane went down in the South Indian Ocean

The most controversial theory: Russians hijacked the plane to Kazakhstan

Electrical failure is another theory

CNN  — 

“Good night Malaysian three-seven-zero.” It was a routine sign-off, an all-is-well.

On March 8, 2014, at 1:19 a.m., someone spoke those last words from Malaysia Airlines Flight 370 to air traffic controllers before the Boeing 777 vanished.

A year later, searchers have no new clues as to where it went with 239 people on board.

Radar and satellite reports have provided hints, but searchers still have nothing to hold in their hands. No wreckage seen floating at sea or beached on shore. No fuselage resting on the sea floor.

Experts have said the data indicate the flight path from Kuala Lumpur, Malaysia, to Beijing unexpectedly veered, putting the commercial jet over the southern Indian Ocean.

But the water’s vast and intricate depths have revealed no secrets. And as clarity has eluded grasp, analysts have made many speculations about what happened.

The most controversial idea: Is the maritime search area all wrong? Did the plane land clandestinely on solid ground?

Here are some expert theories about what happened to MH370. Investigators have since cast doubt on some of their details.

The pilot suicide theory

Who radioed those last words to air traffic control? Capt. Zaharie Ahmad Shah? First officer Fariq Abdul Hamid?

There was much speculation over that, but the Malaysian inspectors in April said it was Zaharie.

The pilots were supposed to check in with new air traffic controllers in Vietnam, but never did. One theory is that one pilot may have incapacitated the other, then guided the plane to its end, taking the passengers down with him in a dramatic suicide.