Via the Huffington Post:

WASHINGTON — Tests performed before the deadly blowout of BP's oil well in the Gulf of Mexico should have raised doubts about the cement used to seal the well, but the company and its cementing contractor used it anyway, investigators with the president's oil spill commission said Thursday.

It's the first finding from the commission looking into the causes of the April 20 explosion that killed 11 workers and led to the largest offshore oil spill in U.S. history. And it appears to conflict with statements made by Halliburton Co., which has said its tests showed the cement mix was stable. The company instead has said BP's well design and operations are responsible for the disaster.

Halliburton reportedly tested the cement mixture four times in February and April but only one of their tests—the last one—proved that the mixture would hold. BP didn't even have the results of this successful test on hand when the blowout occurred—just an earlier test that showed the cement could fail.