A jet crashed at sea after straying off course and losing touch.
Several military planes followed the jet, whose cockpit was vacant.
It crashed Sunday night in Latvia after running out of fuel.
Mon, no survivors were discovered. German and Swedish media identified those aboard as Peter Griesemann, 72, his wife Juliane, daughter Lisa, and a male friend.
Sunday's crash in Latvian seas, hundreds of kilometres from its destination, is unknown.
Nobody was seen in the cockpit or cabin when military planes were dispatched while the Cessna was in flight, a Swedish official said.