British Petroleum (BP) is hoarding information and test results regarding the Deepwater Horizon blowout, said a Transocean’s official on a signed letter.

The letter, signed by the acting co-general of Transocean, Steven L. Roberts, states that the Transocean’s investigation on what caused the oil spill that killed 11 people including nine Transocean employees, is being held back by BP’s refusal to deliver “even the most basic information” about the event.

“[I]t appears that BP is withholding evidence in an attempt to prevent any entity other than BP from investigating the cause of the April 20th incident and the resulting spill,” the letter states, and it goes on to demand a long list of technical documents and lab tests.

BP denied the charge. “We are disappointed that Transocean has opted to write a letter with so many misguided and misleading assertions,” spokesperson Elizabeth Ashford said. “We have been at the forefront of cooperating with various investigations commissioned by the U.S. government and others into the causes of the Deepwater Horizon tragedy.”

The risks are high for the two companies. The Justice Department targets the companies on a criminal investigation. Both companies sent witnesses before an investigatory panel led by the Coast Guard, the Bureau of Ocean Energy Management, Regulation and Enforcement (formerly the Minerals Management Service). A presidential commission is also looking into the oil spill investigation, and is expecting a report on the accident from BP.

Throughout these events, in an effort to plug and kill the well, BP continues to lease a Transocean ship and two Transocean drilling rigs. The situation has become more complicated. After extensive debates, government scientist and BP engineers decided to remove the infamous blowout preventer on top of the well. In that case, BP can assure the government that it can recover the massive contraption without creating new problems with the well.