The BP executive who led the company's probe of the Deepwater Horizon rig explosion denied Monday that his investigators narrowly focused on rig workers' actions to spare onshore engineers and managers from blame for the disaster.

At the start of the second week of a trial over the 2010 oil spill in the Gulf of Mexico, a lawyer for rig owner Transocean Ltd. asked the BP executive, Mark Bly, why his team's report doesn't mention a call from BP rig supervisor Donald Vidrine to an onshore engineer less than an hour before the blast.

Notes from interviews by BP investigators show they knew about a telephone call in which the engineer, Mark Hafle, and Vidrine discussed the results of a crucial safety test that Vidrine allegedly misinterpreted. Hafle told the BP investigators he had warned Vidrine that the results indicated the test may not have been properly lined up.

But BP's September 2010 report says its investigators found no evidence that the Transocean rig crew or BP rig supervisors consulted anyone “outside their team” about the test results.

Transocean attorney Brad Brian pressed Bly to explain that apparent discrepancy. Bly described the call as an “after-the-fact conversation” and said the details of their discussion weren't completely clear. Bly also insisted his team's report covered the test results “pretty comprehensively.”

Brian asked Bly why none of his handwritten notes include any mention of his team's interviews with Hafle.

“Did you just decide not to write it down, sir?” Brian asked.

“I don't recall,” said Bly, whose testimony started last Wednesday.

Vidrine and fellow BP well site leader Robert Kaluza were indicted last year on manslaughter charges and await a separate trial. Their indictment accused them of disregarding abnormally high pressure readings that should have been glaring indications of trouble just before the April 20, 2010, blowout of BP's Macondo well.

The so-called Bly report focused on equipment failures and mistakes that rig workers made. Brian, noting that the Macondo drilling project was over budget and behind schedule, asked Bly why his investigation didn't explore whether the blowout resulted from any decisions that BP made on shore that were designed to save time and money.

“Did you think it was relevant to your investigation whether the people on the shore were making decisions that increased risk in order to save money?” Brian said.

Bly, who was BP's global head of safety before recently announcing his retirement from the London-based oil giant, said BP investigators focused on “engineering trade-offs” and “risk decisions” instead of exploring the costs behind certain decisions.

“It was more driven by the accident we were investigating,” Bly said.

BP accepted some responsibility for the disaster, but its report also assigned blame to Transocean and its other partners on the project.

Vidrine told BP investigators that Transocean crew members had “dismissed drill pipe pressure as anything serious” and had “somewhat joked about my concern over drill pipe,” according to notes from their interview of Vidrine.

The trial opened last Monday and, barring a settlement, is expected to last several months. U.S. District Judge Carl Barbier is hearing testimony without a jury and could decide how much more money BP, Transocean and other companies must pay for their roles in the disaster.

Lawyers for the federal government and Gulf Coast states and private plaintiffs' attorneys hope to convince Barbier that the companies are liable for billions more. BP could be on the hook for nearly $18 billion in penalties under the Clean Water Act if a judge finds that it acted with “gross negligence.”

Barbier also heard testimony Monday by Andrew Hurst, a geoscience professor at the University of Aberdeen in Scotland.

Hurst said a magnitude 6 earthquake struck the area near the site of the Macondo well in April 2006, likely weakening rock formations on the sea floor that already were more fragile than in other parts of the Gulf.

“One has to be very careful with drilling through formations that are very fragile,” he said.

Hurst, an expert in petroleum geology, said he has seen evidence that BP knew about the earthquake before it started drilling the well about three years later.

“They wanted this well to work. It was a real investment,” said Hurst, who wasn't asked to offer on opinion on what caused BP's blowout.

Later Monday, Barbier heard videotaped testimony by Michael Williams, who was Transocean's chief electronics technician aboard the Deepwater Horizon. Williams said Deepwater Horizon captain Curt Kuchta had a “deer in the headlights look” after the blowout.

“He was overwhelmed,” Williams said. “He didn't know what was happening and why.”

In May 2010 testimony before a panel of government investigators, Kuchta testified about a delay in activating the rig's emergency disconnect system. The system, which didn't function after the explosion, allows the rig's “upper marine riser package” to break free from the lower part.

Williams also said the rig's crew members had referred to Macondo as the “well from hell” before the blowout due to difficulties in drilling it.

The trial is scheduled to resume Tuesday with testimony by Randy Ezell, who worked as a senior tool pusher for Transocean aboard the rig. (AP)