Officer D4 is another younger looking dog handler, who appears for the most part to be on the right behind the fountain. Later on he comes further forward. He looks to be in his twenties with close cropped or shaved hair, and of lean build.
D4 also appeared to be involved in the ‘dog attack’ incident on Threadneedle Street shortly before the Ian Tomlinson assault.
[Edited to add links and more information, Thursday 23/4/9]