UPDATE 1-BP removes cap from Gulf well

* Cap atop Macondo well removed

* Next step will be switching blowout preventers (Recasts, adds detail, byline)

By Kristen Hays

HOUSTON, Sept 2 (Reuters) - BP Plc <BP.L BP.N> said it removed a cap from equipment atop its ruptured Gulf of Mexico oil well on Thursday, the first of several steps in advance of plugging the leak for good.

Spokeswoman Jessie Baker said underwater robots removed the cap as planned.

The next step will be to remove a failed blowout preventer on the wellhead and replace it with another. Then BP can resume drilling a relief well that will intercept the blown-out Macondo well and inject mud and cement for a permanent plug.

The failed blowout preventer is key evidence in criminal and civil investigations into the April 20 blowout that led to an explosion aboard the Deepwater Horizon drilling rig and killed 11 men. More than 4 million barrels of oil spewed into the sea.

It will be taken to a NASA facility in Michoud, Louisiana, for forensic study by the U.S. Coast Guard and the U.S. Bureau of Ocean Energy Management, which are jointly investigating the disaster.

"The BOP (blowout preventer) is one piece of evidence that has the potential to provide some answers," the team said on its website.

The U.S. Justice Department also is investigating the accident.

The cap removed Thursday has shut off all oil flow from the leak since July 15.

BP and government scientists believe cement injected into the Macondo well from the top in early August, as well as a seal at the top of the well, will prevent oil from leaking during the blowout preventer switch.

(Reporting by Kristen Hays; Editing by Stacey Joyce)