If it had a root, as was implied yesterday, I'm assuming the prosecution was able to get a DNA profile? I missed the last hour or so of testimony because Lally finally put me to sleep.
I know it took forever for the prosecution to get the hair to the lab and to get it back from the lab, but I don't think even this prosecutor would introduce the hair unless they have an expert who is going to testify that it's John's.
Looking at the clothing though, it's hard to imagine a solo piece of hair being the only genetic material on the SUV that allegedly killed a human being. There was a ton of blood that must have come from the head wound. And I'm sure the defense will point out that the SUV was regularly housed in John's garage.