Does anyone remember this earlier report - citing 'radar'? Since it is still not found, maybe worth re-looking at.
March 8th
The Vietnamese navy had earlier confirmed that Kuala Lumpur-Beijing bound Flight MH370 had crashed into the sea off Tho Chu island.
Tuoi Tre quoted Navy Admiral Ngo Van Phat, Commander of Region 5, as saying that military radar reported that the plane crashed into the sea at a location 246km south of Phu Quoc island.
Vietnam confirms MAS flight crashed into sea off Tho Chu island - The Malaysian Insider