(Kuala Lumpur)  --  Nearly a month after Malaysia Airlines Flight 370 vanished from radar, authorities are launching a criminal investigation into its mysterious disappearance.  The "Wall Street Journal" reports investigators have already taken more than 170 statements with more interviews to come.  One Malaysian police chief says the investigation still may not reveal what happened to the doomed jet.  After more than three weeks, search crews are still coming up empty-handed.  The airliner is believed to have gone down somewhere in the Indian Ocean last month, but there's still no sign of wreckage.  

Officials believe all 239 people on board were lost.  The focus of the massive search has shifted since the plane first disappeared from radar.  More than a dozen countries are devoting manpower and equipment in hopes of finding any sign of the missing Boeing 777.