hereIam - // I still don't understand why they couldn't get DNA. //
As I understand it, the police believe that Mr Lubbock was violated by an object, which may be the pool thermometer which disappeared during the night of the event.
If they could find that, and link DNA from it to DNA from Mr Lubbock, they would have the murderer, but since the item is unlikely ever to be found, they are probably going to have to pursue either a confession, or the evidence from someone who witnessed what happened, and neither have been forthcoming to date.