Many of the world's most developed countries have their own DNA databanks. A sample of every criminal's DNA is taken. If unidentified DNA is found at a crime scene, it can be run through the databank to see if it matches any known criminals.
In the United States, this databank is called CODIS(Combined DNA Index System).
In the United Kingdom, this databank is called NDNAD, or the UK National Criminal Intelligence DNA Database.