A BP internal investigation partially blames the explosion of its Deepwater Horizon oil rig on the company’s own engineers, who made some mistakes when the well was being completed and when reading pressure data that showed the rig was ready to blow. The well’s stability was tested April 20, and BP managers thought the results showed the well was doing fine, and gave employees the OK to replace drilling mud with seawater. The lighter seawater allowed natural gas to move up the pipe toward the rig, where it exploded. The report found that BP—which has tried to spread around blame for the massive oil spill to its many business partners—was at least partially responsible for the disaster. It will be released within the next 10 days.