The Devil's Mask(1946)

A San Francisco airplane bound for South America crashes, and among the scorched debris is found a shrunken native human head, neatly packaged. The perplexed police contact a local anthropology museum about this unclaimed piece of grisly baggage, where they intersect with Jack and Doc, two private eyes, called there to meet a mysterious woman who had a case for them and wanted to meet in private.