ALBANY, N.Y. (AP) — Federal safety investigators say their attempt to get to the bottom of the nation's deadliest transportation wreck in nearly a decade is being stymied by a prosecutor in upstate New York.

In a letter made public Thursday, the National Transportation Safety Board said it still hasn't gotten full access to a limousine that crashed in Schoharie County in October, killing 20 people.

An NTSB lawyer told county District Attorney Susan Mallery that "safety-critical evidence" has been lost because of its inability to inspect the vehicle.

Mallery's office didn't respond to a request for comment, but told WRGB-TV in Albany the limo is evidence in a negligent homicide case against its owners.

The Associated Press previously reported that investigators were privately expressing frustration over their access to the wreck.

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