Authorities are taking a deeper look at the lives of the passengers and crew of Malaysia Airlines Flight 370 after hundreds of interviews and background checks yielded no likely suspects in the investigation of the plane's disappearance.

The past week of searching for wreckage in the Indian Ocean turned up only items unrelated to the plane, and without any direct evidence of how the plane disappeared, investigators are redoubling efforts to determine who could have been involved in the "deliberate act" officials...