Engineering experts probing the Gulf of Mexico oil spill exposed holes in BP's internal investigation as the company was questioned Sunday for the first time in public about its findings. BP's lead investigator acknowledged that the company's probe had limitations...[T]he National Academy of Engineering panel noted that the study avoided organizational flaws that could have contributed to the blast...BP's study found eight separate failures led to the oil rig accident. The report blamed BP and other companies, including Transocean, the rig's owner, and Halliburton Co., which was hired to do the cement work...When asked why Halliburton continued to work on the well despite some of these red flags, Roth said, "We didn't see it to be an unsafe operation as it was being executed."