Well, I thing you could exsume him and look for some kind of remains of blood. But I am sure your not THAT curious.
In any case, I looked up and it seems you would need the blood types of both parents' blood types to test parentage with blood types.
http://www.bloodbook.com/inherited.html
Of course, I am not a doctor or even a medical student; I am just a college student, sho I would go seeking more expertly opinions before I would do anything.