Good question! And while I have no idea, I bet some of it depends on the geographical area. I think of cases in rural areas (following one now in the US), and they are absolutely looking for a body. There is so much ground to cover and vast areas. So, there are a lot of dogs involved, etc. In a more urban area, I think they hope to find the person but are probably much more likely to find evidence as well, in a relatively small area like a park or the area around a bench - as opposed to miles of orchards or forest. And there's no cctv on miles of country roads!