If they can find his dentist, they could compare the corpse's teeth against dental records (X-rays). They could also compare other physical attributes, such as

If they can find his dentist, they could compare the corpse's teeth against dental records (X-rays). They could also compare other physical attributes, such as height, gender, etc. If he has close relatives (parents, siblings, children, etc.), they could compare the corpse's DNA against theirs and conclude that it was likely/unlikely/impossible that the corpse was related to them.