Almost a century after Phillis Symons was murdered and buried in an unmarked Karori grave, a headstone mysteriously appeared.

Symons, 17 and pregnant, was killed by George Errol Coats in June 1931 and buried - some say alive - in the dirt excavated to build the Mt Victoria tunnel, where her body was later discovered.

Historian Gabor Toth says it's a mystery as to how the headstone got there.

"The fact that her grave has been unmarked has been remarked upon over the years - I do know that the Friends of Karori Cemetery, a group that got going about five or six years ago were actively engaging with Phyllis Symons' family over in Australia and they were working towards getting a gravestone...but this isn't it."

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