NEW ORLEANS — Over six days in May, far from the familiar choreography of Washington hearings, federal investigators grilled workers involved in the Deepwater Horizon disaster in a chilly, sterile conference room at a hotel near the airport here. The six-member panel of Coast Guard and Minerals Management Service officials pressed for answers about what occurred on the rig on April 20 before it exploded. They pushed for more insight into an argument on the rig that day between a manager for BP, the well’s owner, and one for Transocean, the rig’s owner, and asked Curt R. Kuchta, the rig’s...