The “blowout preventer” from BP’s Macondo well — which infamously failed to prevent this summer’s spill — has begun its transition from subsea equipment to federal evidence.

The 450-ton device was removed Friday afternoon from the Gulf of Mexico floor and attached to a long section of pipe that will be used to haul it 5,000 feet to the surface, according to a statement from retired Coast Guard Adm. Thad Allen, the federal government’s point man on the BP oil spill.

Allen said it would take 24 to 36 hours for the device to reach a rig called the Q4000. The removal of the blowout preventer had been delayed because of high waves in the Gulf, which would have put extra strain on the pipe; it was carrying about 1 million pounds.

When it is brought to shore, the device will undergo the mechanical equivalent of an autopsy. Federal investigators will take the blowout preventer apart as they try to determine why it failed to shut off the well after the explosion at the Deepwater Horizon rig April 20.

If the device was poorly maintained — or altered in a way that made it less effective — that could contribute to a finding of criminal negligence against BP or one of the contractors working on the rig. The investigation could also find that improperly attached pipes shot up into the device during the blowout, jamming it open.

The BP well has not leaked oil since July 15, when remote-controlled submarines sealed shut a mechanical “cap” that had been installed on top of the blowout preventer.