CHARLESTON, W.Va. – Federal investigators arrived Monday at the West Virginia mine where 29 men died in an explosion last week to begin piecing together what caused the worst U.S. coal mining disaster since 1970.

Hundreds of mourners including the governor observed a moment of silence at the state Capitol, during a wreath-laying ceremony at the foot of a statue honoring the state’s miners.

Karen Barker of Charleston was among scores of state workers who attended. “My dad was a miner and my grandfather was a miner. I have no idea how these people feel about losing their family member, but I can imagine,” she said.

Virginia Gov. Bob McDonnell also asked people in his state to observe the moment of silence. President Obama ordered all U.S. flags in West Virginia flown at half-staff until sunset Sunday.

The inspectors at the Upper Big Branch mine weren’t heading underground until searchers removed all the bodies from the mine. The last bodies were expected to be taken out Monday. Recovery efforts had been stalled in previous days by volatile gases, but teams entered after the tunnels were ventilated.

The state panel that writes mining safety rules and typically reviews inspectors’ reports after the investigations are complete said it would like to join the investigators underground.

Richmond, Va.-based Massey has been under scrutiny for a string of safety violations at the mine, although 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.