CHARLESTON, W.Va. (AP) — The bodies of all 29 West Virginia coal miners killed in an explosion last week have been recovered from the mine, a spokeswoman for the state mine office said Tuesday.

Jama Jarrett said the last bodies were taken out around 2 a.m. or 3 a.m. Tuesday and the bodies were being sent to the state medical examiner for autopsies.

Recovery efforts had been stalled in previous days by volatile gases, but teams entered after the tunnels were ventilated.

Federal investigators have begun looking into what caused the worst U.S. coal mining disaster since 1970.

The team of inspectors from the Mine Safety and Health Administration briefed Secretary of Labor Hilda Solis and MSHA director Joe Main at the Upper Big Branch mine Monday.

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The mine’s owner, Richmond, Va.-based Massey Energy Co., has been under scrutiny for a string of safety violations at the mine, though CEO Don Blankenship has defended the company’s record and disputed accusations that he puts profits ahead of safety.

Authorities have said high methane levels may have played a role in the disaster. Massey has been repeatedly cited and fined for problems with the system that vents methane and for allowing combustible dust to build up.