NGB1066 is there any way the DNA could have been planted or contaminated?
It is theoretically possible but in the context of the case highly unlikely. Mike Mansfield did his best to advance the contamination argument. He based it on the fact that the exhibits had got mixed up over the years and not looked after as they would be now. In particular there was a phial in the exhibits which was broken at some stage. It may have originally contained semen samples taken from Hanratty's trousers following his arrest. It was argued that this might have contaminated Valerie Storie's knickers. This could not be excluded as an extremely remote but theoretically possible event. However, the only staining on the knickers containing DNA was that of Hanratty and Michael Gregson, (Valeries's murdered boyfriend) even though there was other extensive staining (I am sorry to be so explicit, but it is necessary in order to explain). It was beyond belief that if Hanratty was not responsible there was no trace at all of the DNA of the rapist. At the end of the day anything is a theoretical possibility, but the odds here are absolutely overwhelming against Hanratty.
This was a major blow for Paul Foot who campaigned for many years on behalf of the Hanratty family. Even after the final appeal he found it very difficult to accept, although I understand that he did contemplate before his death that he may have been wrong.