All four of the witnesses scheduled to testify at today's hearings to investigate the Deepwater Horizon disaster “declined to voluntarily appear” before the joint Coast Guard and Bureau of Ocean Energy panel, resulting in a cancellation of today’s hearing.

Tuesday night, two of the Transocean witnesses “bowed out saying they needed more time to review documents discovered in the investigation,” according to the Houston Chronicle. The other two postponed “due to an apparent conflict of interest with their attorney,” who also represents Transocean’s chief engineer.

“All four Transocean officials were issued subpoenas,” the Marine Board said in a statement announcing the cancellation. “Due to the fact that the witnesses did not reside within the specific geographic jurisdiction of the investigation, the board cannot compel them to appear.”

Earlier this week, two BP witnesses also were no-shows at the hearings. Both Donald Vidrine and Robert Kaluza, BP employees in charge on the rig, declined to appear for a second time after missing the hearings in May. Vidrine again cited medical reasons, and Kaluza invoked his Fifth Amendment right against self-incrimination.

The four Transocean workers who declined to appear at today's hearings were all blowout preventer supervisors. The blowout preventer is a key piece of safety equipment that failed at the Gulf well, leading to the worst environmental disaster in U.S. history.

In Tuesday’s hearing, a BP employee testified that leaks were found on the blowout preventer two weeks before the accident, at which point BP was supposed to—but did not—stop the drilling work. Monday's hearings focused on some of the "excessive" maintenance lapses aboard the rig, which BP has said is the responsibility of Transocean.

According to Bloomberg, the panel has already designated five Transocean workers as “parties of interest,” meaning they could face criminal charges for decisions that led to the accident, which killed 11 Transocean workers. Guy Cantwell, a Transocean spokesman, declined to comment to Bloomberg on the investigation.

On Tuesday, the panel also released a list of warning signs—20 so-called “anomalies”—with the well in the hours before its blowout on April 20. You can check out that list in our document viewer.

The hearings are expected to resume Thursday and Friday.