(CNN) -- A blowout preventer that may hold important forensic evidence as to why it failed, triggering the world's largest accidental oil spill, has been brought to the surface of the Gulf and placed on a vessel, officials said Saturday night.
The device "was taken into custody by the U.S. Department of Justice as evidence in its ongoing investigation into the incident," BP said. The blowout preventer was lifted to the surface at 8:53 p.m. (9:53 p.m. ET).
Adm. Thad Allen, the government's national incident commander, said the huge blowout preventer "is considered evidentiary material."
The April 20 explosion killed 11 workers aboard the Deepwater Horizon rig.
A new blowout preventer was installed atop BP's plugged well late Friday.
Crews had to flush out potential hydrates -- crystals that form in cold temperatures -- before the old blowout preventer was hauled about the Q4000 surface vessel.
Joint investigation teams, engineers and the Department of Justice will pore over the recovered device.
"I'm very pleased to announce that with the new blowout preventer on [and] the cement that was previously put in ... this well does not constitute a threat to the Gulf of Mexico," Allen said earlier Saturday.
He provided details on the installation of the new blowout preventer late Friday.
"This is an important milestone as we move toward completing the relief well and permanently killing the Macondo 252 well," he said.
Once the new device is successfully tested, BP will drill the last remaining feet of a relief well to intercept the damaged well.
Finally, the company will execute a "bottom kill" -- a measure that fills the well from the bottom with mud and cement. That is believed to be the only way to seal the well for good.
"Depending upon weather conditions, mid-September is the current estimate of the most likely date by which the relief well will intercept the MC252 well," BP said in a statement Friday, using the shorthand reference to the well's official designation, Mississippi Canyon Block 252.