Modern day indigenous Australians say that Captain Cook's men "stole" spears from the aboriginals they met at Kamay.

Wikipedia (I don't have access to a better reference) transmits a report from the other side: that the aboriginals at Kamay fought with the British sailors each time those landed. The term "steal" does not fit that sort of situation.

Either or both accounts may be distorted, but I see no reason in the article to endorse the indigenous interpretation of "stealing", and no obligation to "return" the spears.