According to documents obtained by the Houston Chronicle, the Transocean employee has manipulated equipment on the 50-foot-tall, 300-ton blowout preventer, while a government contractor runs it through a battery of tests in New Orleans.

Transocean owned the Deepwater Horizon, which included the blowout preventer, and BP leased the rig to drill its doomed Macondo well.

Because the testing is essential to learning why the blowout preventer didn't work as planned, the Transocean employee's involvement raises "serious questions as to the credibility and objectivity" of the government's investigation, said Rep. Ed Markey, D-Mass., who heads a House Energy and Commerce subcommittee that has taken a lead role in probing the disaster.

"If we are to hold the companies legally responsible for this accident, we can't afford any black mark on the investigation involving the 'black box' of this underwater disaster," Markey said in a letter Tuesday to Michael Bromwich, director of the Bureau of Ocean Energy Management, Regulation and Enforcement.

Former supervisor

The bureau and Coast Guard are jointly investigating the Deepwater Horizon disaster and are overseeing the autopsy on the blowout preventer that began in mid-November.

It was recovered from a mile below the surface of the Gulf of Mexico after engineers finally sealed the Macondo well that blew out, destroyed the Deepwater Horizon and spilled millions of gallons of crude into the Gulf of Mexico.

The government contracted the forensic analysis firm Det Norske Veritas to run the equipment through tests designed to shed light on why key pipe-cutting and hole-closing components failed to slash through drill pipe and seal off the well hole.

DNV later arranged for Owen McWhorter, onetime subsea supervisor on the Deepwater Horizon, to assist in the testing.

The government instructed DNV to terminate its contract with McWhorter after concerns were raised last week by the Chemical Safety Board, a federal agency also investigating the disaster.

The decision to use the Transocean employee as a consultant appeared to violate a conflict-of-interest provision in the government's contract with DNV, acknow-ledged Michael Farber, a senior adviser for the ocean energy bureau, in a letter to the Chemical Safety Board.

Public confidence

Board Chairman Rafael Moure-Eraso had said that while McWhorter wasn't on the rig when it blew up, he "still had responsibility" for the blowout preventer in the preceding weeks and months.

"While the CSB is not aware of any specific actions by Mr. McWhorter that would compromise the evidence, the effort by the (joint investigation team) and DNV to provide him with unique access to the testing could undermine public confidence in the quality, independence and reliability of the whole enterprise," Moure-Eraso said in a Dec. 13 letter to the ocean energy bureau.

Photos of the testing space obtained by Hearst Newspapers show a man identified as McWhorter manipulating a pipe ram on the blowout preventer and working with other equipment on the device over at least a two-week period beginning as early as Nov. 23.

McWhorter could not be reached for comment.

Limited access

Access to the testing space is limited to DNV workers and one representative each for key stakeholders, including BP, Transocean and Cameron International, which manufactured the blowout preventer.

The Chemical Safety Board and the Justice Department, which are leading separate investigations of the disaster, also have access, as do the plaintiffs in a broad spill-related lawsuit.

According to the testing plan agreed to by those stakeholders, their representatives aren't allowed to manipulate the blowout preventer and only one at a time is allowed inside the primary test area.

jennifer.dlouhy@chron.com