Some clarity!! Thank you!!!!
They can also interview them, observe their behavior and find out if they my have inadvertently alerted sketchy people to Nancy being alone at night.Doesn't really reveal they have DNA from an unknown source inside the home. Just reveals that NG's hired associates are submitting DNA samples. And likely voluntarily in case they do find unknown DNA in the home and want to distinguish it from known DNA (so that they can rule out or scrutinize it more).
JMO.