its really a bad idea to think that there is one cause for any engine to blow unless the cause is blatantly obvious. in the thread where kyle (ms3guy22) talked about his motor blowing, i addressed more than a few things which i felt could have been the issue. an internal combustion engine is a complex machine and as such its not always simplistic reasons, one or few, that do a motor in. often times its a chain reaction or combination of bad choices/occurrences.
case in point, people are popping these motors stock, no mods, and this has been posted more than a few times. we've seen one guy here with a mazdaspeed3 who has gone through two engines in less than 10k miles. if you want a root cause out of any of that, it seems damn simple to me despite the fact that people are unwilling to accept it; these engines are not incredibly strong and they are certainly not bulletproof. i don't know how many pictures can be taken of the rods when they bend, when they snap, of holes in the block, of shredded bearings, of cracked pistons. all other things aside, its really annoying and ignorant to see people rant and rave about the DISI's fabulous forged rods when they snap, curl, twist or bend. Forged or not, polished turd or not polished - they're still turds and in no way should people have confidence that they are going to make 350whp plus, reliably, long term on them. it does not matter if they are forged or not when they are simply not beefy enough in and of themselves. it would be well advised for people to get the notion that simply forging a part makes it indestructible, much in the same respect that a "perfect air fuel ratio" makes an engine unblowable.
alot of things can happen. personally from the videos i saw before this particular engine blew, i believe the crank walked and spun a rod bearing. eventually when the bearing dissolves completely the rod is going to bust free and find another place to go, and on an aluminum block its pretty easy for a rod flying around in the cylinder at 6000rpm to make a dramatic exit.