While we would get a better answer probably this week, I would like to point to 3 "evidences":
-several eyewitness reported increasing sound of the engines short of the impact. One supposed eyewitness (on the ground) said: "There was no explosion but the noise of the impact, a big bang, the ground trembled and
there was the sound of engines howling like they reversed power or were just overturning by lack of resistance.*" "*Jeroen Jonkers, an Amsterdam resident, is an eyewitness of the crash of a Turkish Airlines flight in Amsterdam. He contacted Hurriyet Daily News via its website and sent his story. This is his story in his own words."
http://arama.hurriyet.com.tr/arsivnews.aspx?id=11090641 (I know, maybe not the best source, but I think a detached, running, engine would make a very particular noise and the description doesn't sound like a fake).
-then this picture, from the highway, showing the
first seconds after the impact, with dust "traces" from the engines. The engines nearly 80-100 m in front of the plane wing (aparently)
http://media.nu.nl/m/m1bzv76a43o6.jpg
There are a lot of pictures showing both an engine and the plane, but taken with telephoto lens (or similar zoom) that gives a wrong distance feeling ("the telephoto shot appears to compress the distance between objects due to the perspective from the more distant location." Wikipedia).
-Both engines apparently travelled the same distance and one remained in the same "flight" direction. I tend to think it was due to gyroscopic effect.
Well, that's all my speculation and I would wait the DFR and CVR readings.
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