There are some proofs to rumors that landing gear lever was pulled before leaving runway:
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An employee of this company Miroslaw Lawrynowicz said that the cause was human error accident. - .
During the run, after lifting the front wheel, the flight engineer retracted gear- said Lawrynowicz
Wprost 24 - Awaria polskiego samolotu w Tallinie
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Rescue chief of TLL Toomas Mardo said that after aborted takeoff the plane skidded approximately 1km along the runway. He saw the incident and described that there was a fire of sparks emitting from belly of the skidding plane. It was kind of miracle that the plane didn't catch the fire and everybody got out of the plane without any injuries.
Pictures of removing the plane from Runway.
http://pilt.delfi.ee/album/187063/