Remember how they got the guy who murdered Daniel Morcombe.
This to me is all theatre directed at one person, manipulating their next move. The suspect may not know what the sister has told LE, (I assume she has been questioned recently) and if the Morcombe sting is anything to go by, LE are not above going to elaborate lengths to get a confession. That includes, providing the suspect with a plausible manslaughter confession, and publicly showing the suspect steps that LE would plausibly believe.
This is all too public. Show me one example that we have of police using a blacklight and the public have open access to viewing it. They put tarps up, sheets, block off roads. Its a cul-de-sac, very easy to manage access. Those photos are not a photographer hiding in a tree with a telescopic lens. Come on.