It was the dog "Brock" who led his owner and handler Louise Holmes to the dead body of Dr David Kelly at about 9.15 on the morning of the 18th. Brock was entered for the Crufts "Friends for Life" competition in 2009. Not only was he entered but he went on to win it! The benefit for this blog is that there are youtube videos of him and Louise Holmes such as these two:
I found the explanations written below the first of these videos very interesting. It includes mention of a lady with alzheimers who wandered off from her home. Brock was able to track her from her house through the streets some hours after she had gone missing. That raises in my mind the question of just how long the scent remains "live" after the person being searched for was at that particular point.
In the quoted example it looks as if Brock familiarised himself with that lady's scent at her home and then followed the route she took without being distracted by other smells. On the 18th July 2003 though we are told that Brock found the body of Dr Kelly in an "air scenting" exercise. In other words there is no indication that he, for instance, was given an item of Dr Kelly's clothing to smell before searching.
This article gives some explanation of air scenting and how dogs are trained to productively use that ability http://suite101.com/article/search-and-rescue-dog-training-air-scenting-a106740
One theory is that Dr Kelly was carried in to the wood. If this was the case then I suspect it was at some fair time before Brock arrived because no evidence was given of him being distracted by any other scents. The scents of any "stretcher party" bringing Dr Kelly into the wood would have melted away I suppose before Ms Holmes and Brock made their discovery.