Heard on the news this morning that they did find a fatique crack on the broken wing
It remains to be determined if that crack was the cause of the crash. Lots of planes develop fatique cracks over the years. Not all cracks lead to structural failure and most aircraft structures are designed to avoid catestrophic failure. The plane had just taken off and was climbing. Neither of those are exactly high stress (on the structure) operations although the engines are putting out full power.
It'll likely be months before we know for sure.