Today's DNA screening is a last resort for Sussex Police who have interviewed more than 9,500 people as part of the extensive inquiry into the murder of Valerie Graves.
A BBC Crimewatch appeal and a £20,000 reward have failed to yield any suspects or charges.
On the first-year anniversary of the murder last month, officers handed out leaflets and put up posters about the DNA screening.
Graves' death shocked the small community of Bosham, which featured in an episode of the ITV crime drama Midsomer Murders.
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