Well then it would give me pause, depending on what it was found on. However, until and unless the donor of the DNA is identified, I will continue to base my theories on the people I KNOW were in the house.
Just off the topic of JBR a little, but on the issue of unknown DNA. I was looking into some unsolved child murders here in Oz and came across a website dedicated to three siblings, the Beaumont Children, who went missing in 1966. Aside from some sightings of the children with a man, there has been absolutely no trace of the children ever found and no forensic evidence. The murders brought to an end to the innocence of children in Australia, when mum would send you off to play, with only the proviso of getting home before dark!! Suddenly parents wanted to keep children within sight.
There are four main suspects, none of these can be proven to have been in the city where the children disappeared, but neither can any of them be ruled out. At least two of these boasted that they had murdered the Beaumont children. One of these four suspects was declared criminally insane, and he is suspected to have committed several other child murders, (which could be proved/disproved with DNA) but because he has never been convicted, he cannot be compelled by law to provide a DNA sample.
I think of each of these suspects, who could have all committed the murder of the three children, in relation to the murderer of JBR.
Did he die before he could commit other murders.
Had he committed other murders that were not linked to JBR but none since.
Has he committed murders before and since but has never been caught.
Was he never convicted due to insanity or is he in a mental institution for other reasons.
Is he in jail for some offence that doesn't require his DNA to be taken.
Was her murder a one off and the perp has never committed another.