Interesting wording in that article.
First: "That sample connected Matthew to a 2005 sexual assault in Fairfax County, a Virginia suburb of Washington D.C., according to authorities."
Then: "The DNA evidence in the Fairfax sexual assault, in turn, linked Matthew to the Harrington case, authorities have said."
That would imply that the DNA evidence in the Fairfax assault case that linked to the Harrington case did not come from JM? Otherwise why not just say that his DNA was directly linked to the Harrington case.