Next month will mark the eighth anniversary of one of the most shocking crimes ever committed in Ireland.
Alan Hawe killed his wife, Clodagh Hawe, and three sons - Liam, Niall and Ryan - in Castlerahan in 2016.
A forensic detective who was involved in the case has written a book about his career, called Identity. John Sweetman writes about the Hawe case in detail.
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He has been speaking to Eoghan Murphy, firstly about how he became a fingerprint and handwriting expert.