Although high profile, it started off as very much a cold case review. Perhaps more able and ambitious officers didn't want to take it and it fell to a less officer, winding down towards retirement.
A safe pair of hands who could be expected to do as he was told and not rock the boat, perhaps.
Hamish Campbell had a long career with the Met. He joined in 1974 and left in May 2013. He attended the same university as Redwood and gained the same degree. Campbell's was gained in 1995-1997. I don't know when Redwood got his. In January 2009 he joined the Homicide and Serious Crime Command. In May of the same year Redwood joined that department too.
In December 1999 Campbell was appointed as the investigating officer on the Jill Dando case, Operation Oxborough. At the time the investigation was growing cold after seven months. The new team got a result; Barry Bulsara was arrested and convicted.
Campbell retired in May 2013, Redwood in December 2014. It seems Nicola Wall replaced Campbell as the Senior Investigating Officer, despite being a DCI as opposed to Campbell's rank of DCS. I wonder if she has an Investigating Officer to replace Redwood or if that position has become redundant?