Evidence of negligence before the April 20 explosion on the Deepwater Horizon oil rig continues to surface in advance of Wednesday’s House Energy and Commerce hearing about the cause of the blast.

A worker for the rig’s owner, Transocean, told Coast Guard investigators: “I overheard upper management talking saying that BP was taking shortcuts by displacing the well with saltwater instead of mud without sealing the well with cement plugs, this is why it blew out.”

The seawater was meant to contain pressure in the well, and statements from other workers confirmed that pressure levels were abnormal shortly before the blast, the Associated Press reports.

What began as a routine pressure problem, however, suddenly turned to panic. The workers called bosses to report a situation, with assistant driller Stephen Curtis telling one senior operator that the well was “coming in.” Someone told well site leader Donald Vidrine that they were “getting mud back.” The toolpusher, Jason Anderson, tried to shut down the well.

It didn’t work. Both Curtis and Anderson died in the explosion.

An internal BP investigation submitted to Congress said that tests less than an hour before the explosion found a buildup of pressure that was an “indicator of a very large abnormality.” But another test satisfied the crew’s concerns, and they resumed filling the well with seawater.

At least 7 million gallons of crude oil has leaked into the Gulf of Mexico since the explosion on the Deepwater Horizon.

Gulf Oil Spill: Effort to Seal Leak May Be Delayed, Disputes Over Dispersant