Three employees of Transocean, owner and operator of the Deepwater Horizon, have refused to cooperate with a federal investigation into last year’s Gulf of Mexico oil disaster.

The U.S. Coast Guard and the Bureau of Ocean Energy Management, Regulation and Enforcement are together conducting hearings in New Orleans on why the oil rig’s blowout preventer failed to stop the April 20, 2010, accident that killed 11 workers—nine of them Transocean employees— and spewed nearly five million barrels of oil into the ocean.

Michael Bromwich , director of the ocean energy bureau, said the employees’ refusal to testify was “unacceptable” and that Transocean should punish them for not cooperating.

A company spokesman claimed that Transocean was not responsible for two of the employees, James Kent and Jay Odenwald, because they have hired their own lawyers to represent them.

Bromwich, in turn, responded that “this is less a legal issue than one whether Transocean recognizes its moral and corporate responsibility to cooperate with an investigation into the causal factors of the most significant oil spill in Untied States history.”

At the time of the Deepwater Horizon accident, Kent was Transocean’s asset manager in charge of the rig that exploded. Odenwald, a senior subsea engineer, was in charge of the blowout preventer that failed.

The third Transocean employee who has refused to testify is Geoff Broughton, who served as the company’s representative during a four-month investigation that concluded the blowout preventer failed because the force of surging oil and gas caused a drill pipe to buckle and bend, stopping the preventer from covering the well hole.

A Transocean lawyer told the government that a senior technician would be sent to the hearings to answer general questions about the design, maintenance and performance of the blowout preventer.

-David Wallechinsky, Noel Brinkerhoff