DNA used in a criminal case

[Margaret in Burton]

In Burton on Trent in 1971 the body of a young man was discovered buried in the remains of a flint mill by the river Trent. This has become known as the case of Fred the Head as his head was the first thing uncovered. Nothing is known about him. He was found naked except for some socks and wearing a ladies wedding ring on his ring finger of his right hand. The ring was hallmarked 1968/9. It’s been suggested he was gay. DNA in later investigations said he might be from Eastern Europe.
A anthropologist friend of mine has suggested to the police investigating this cold case that an isotope scan of a tooth now may reveal more.

In this country can DNA be used from police cases on commercial sites to find possible relatives and how?