To be absolutely 100% safe, you'd have to say the aircraft broke up somewhere between 37,000 feet and the bottom of the ocean. I don't believe for a minute it landed intact and broke up as it sank, but I'm not sure we can conclusively rule it out (anyway, ships often break up on the way to the bottom).
I suspect the recovered debris contain the information needed to determine where the break up occurred. But the pictures of the debris may not.