HOUSTON (AP) — A critical device at the center of an investigation into the Gulf oil rig explosion didn’t undergo a rigorous recertification process in 2005 as required by federal regulators, a worker responsible for maintaining the equipment told investigators Wednesday.

Mark Hay of rig-owner Transocean said the blowout preventer — designed to prevent a spill in the case of an explosion — was not recertified because it was being constantly maintained. Recertifying the five-story device requires completely disassembling it out of the water and can take as long as three months to complete.

The device — which may be lifted from the seafloor a mile below the water’s surface in the coming days — failed following the rig explosion.

After the blowout, some 206 million gallons of oil spewed into the Gulf until mid-July, when a temporary cap stopped the flow. A permanent fix is expected to be put in place after Labor Day.

The blowout preventer will be key to the investigation into the April 20 explosion that killed 11 people and caused the biggest oil spill in U.S. history.

Testimony from BP and Transocean officials showed the device had not been recertified according to a three- to-five year timetable laid out by federal regulators; repairs were not always authorized by the manufacturer, Cameron; and in the days after the explosion confusion reined about changes to the equipment, delaying attempts to close the well.