Sources close to the process said investigators were also examining whether BP executives, including former CEO Tony Hayward, made statements that were at odds with what they knew during congressional hearings last year.
The U.S. justice department opened criminal and civil investigations into the spill last June, filed a civil lawsuit against BP in December but has yet to file criminal charges.
Authorities are investigating BP managers who worked both on the rig and onshore to determine whether they should be charged in connection with the workers' deaths. The investigation aims to determine whether BP managers' decisions to cut costs and fast-track the project led to fatal safety sacrifices.
In addition to the testimony of Hayward and others before congress, investigators are reviewing emails and other documents to determine what BP officials and Deepwater Horizon partners knew when they testified last June.
In January, a presidentially appointed national commission filed its report on the Deepwater Horizon spill and concluded that the "explosive loss" could well have been prevented. In a final report Commission Counsel Chief Fred Bartlit laid considerable blame on BP.
Bartlit said BP was aware of problems with lab tests of Halliburton cement used to seal the well for three years but that BP decided not to install a safety device known as a lockdown sleeve in order to save five-and-a-half days and $2M (£1.2M) in costs. He also said BP's well-site leader missed a critical test known as a negative pressure test that indicated something was wrong, a test he should have supervised.
Read Coast Guard's report
