The owner of the rig that exploded in the Gulf of Mexico has told federal investigators that the now infamous blowout preventer is in danger of corroding and its value as a key piece of evidence may be compromised.

Transocean lawyer Steven Roberts said in a Nov. 3 letter to the federal investigation team that forensic testing had not yet begun on the device even though it's been sitting at a NASA facility in New Orleans for two months. He said it may be corroding because of inadequate preservation.

The letter was obtained Wednesday by The Associated Press.

A spokeswoman for the investigation, Eileen Angelico, declined to address the specific claims by Transocean when contacted by the AP, but she said investigators are "committed to preserving, securing and examining the evidence in accordance with standards developed in consultation with the Department of Justice and the Federal Bureau of Investigation to ensure that they will withstand the highest standard of judicial scrutiny."

The device failed to stop oil from gushing into the sea following the April 20 Deepwater Horizon explosion.

The blowout preventer, which Transocean was responsible for maintaining while it was being used on BP's well, was raised from the seafloor on Sept. 4. It was taken to the NASA facility a week later.

Investigators agreed to flush the control pods with fluid on Sept. 27 to prevent corrosion. But Roberts said in his letter that there have been no further preservation steps on the blowout preventer since then.

The investigation team has previously asserted that it hadn't begun testing because of the time it was taking to develop procedures for the testing. Last month, a memo from the investigators to interested parties said final protocols would be submitted to the team for approval around Oct. 15.

There has been no public word of the status of testing since then, and in his letter Roberts said he is still seeking that information.