Current speculation (and of course, it is only speculation at this stage) was that they ran into sea fog. This would suggest loss of control after inadvertantly entering IMC. Given the terrain around there (coastline with wide, flat, open beaches), spatial disoriantation is the only explanation I can come up with for such mangled wreckage (other than a control failure, I suppose). If this was indeed the cause, they are probably lucky to be alive at all.
If there was decent visibility, an engine failue or most any other mechanical issue would be a complete non-event almost anywhere in Holland. The country is so flat and open, you're always spoilt for choice with regards to an emergency landing.
Let's hope the people involved can report what happened themselves very soon.