I agree , kinda of setting wherein all kinds of stuff, blood, body parts etc are all evrywhere - would be pretty hard to say with certainty what came from where.
Yes, but if KT's DNA is found on any component...she will have some explaining; especially if it is an inside part or a discarded part of a component. She supposedly was at work so her DNA should not be found on anything retrieved at the marathon site- except maybe the outside of the pressure cooker or backpack which she could have innocently touched.