these planes are sort of constructed in three big pieces...the front part, the middle part and the tail part ...so, it seems we have found the big parts and they sort of break up that way.
Not always right and not exactly right. But certainly one of the things I look at, from the start of an investigation. In manufacturing they are often called "production breaks". Not always right and not exactly right - and rather simplified - but production break 'lines' are often 'stronger and stiffer' than the areas on either side. So the probability is high that the breaks are on one or either side of these 'lines', and the probability is low that 'through the line itself' is the break. The recovered tail section can be used as a case study. It shows technically important fracturing details.
Note that the production breaks that you mention are on the 'highest level'. Depending on the complexity and design date of the aircraft, there are a number of levels below that. A section break is not the same as the production break/interface of a fuselage panel for instance. This subject is a sub-part of the so-called "interface management". For all kinds of reasons there is a complex relationship between interface management and configuration management. I said something in my previous post about the latter subject.
Let's hope they find the missing passengers and crew in the recently discovered sections.