I think it’s the pipe that cased the BOP to fail.
Could very well be true. I've read that BP only put in 4 things that center the casing in the hole, Drillers and cementers wanted 3 times that many since this was a "problem" well. Might very well turn out that casing failure resulted from poor drilling practices by BP.
I've followed investigations into airline crashes. It almost always turns out that a series of small mistakes, poor practices and a little bad luck lead to a catastrophic failure. I'll bet dollars to donuts the same will be true here.