Investigators working to learn what caused a vintage de Havilland Otter to crash Monday killing five people including former U.S. Sen. Ted Stevens have finished examining the wreckage at the crash site, a top official said Thursday.

But they are still early in their investigation, with many records to collect and people to interview, said Deborah Hersman, chairwoman of the National Transportation Safety Board.

Nine investigators from the NTSB are working the case including two in Dillingham near where the crash occurred, Hersman told reporters at a late afternoon briefing.

The crash also injured four people. Stevens and the other passengers were on a GCI plane that took off from a company lodge on the Agulowak River north of Dillingham sometime Monday afternoon. Investigators are still trying to pin down the time.

The group was headed for an afternoon of silver salmon fishing on the Nushagak River, but the plane smashed into a mountain in the Muklung Hills range. Assuming they didn't detour after leaving the lodge, the wreck would have happened about 15 minutes after takeoff, Hersman said.

Investigators went to Providence Alaska Medical Center Thursday morning to attempt to interview some of the four survivors, but the patients weren't ready, she said. Sean O'Keefe, former NASA head, was still in critical condition while his son, Kevin, and Jim Morhard, a lobbyist, had been upgraded to fair. The youngest person on board, 13-year-old Willy Phillips, was in good condition.

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