The DNA database, unlike the fingerprint database, is not just used to search for exact matches, it is also used to search for “potential suspects”.
For example, if the police search the database and find no results based on the sample they have, they can then re-search it for “familiar”, the aim is to find a person who may have family who could be responsible.
Once a people with matching DNA has been identified a long list of names is produced, and from this, and ‘traditional police methods’, e.g assumptions on age, geography, ethnicity, etc this can be narrowed down to a list of families, upto 150. These families will then be contacted, and where possible questioned/investigated further. This by its very nature could cause the police to disclose that an individual has a criminal past, no matter how minor, or how long ago, to people who previously did not know.
“….., the database is used for ‘familial searches’. If a DNA crime scene sample is loaded onto the database and does not ‘match’ any individual’s profile, the police will sometimes search for close matches in order to narrow down a list of possible suspects. They hope to identify a family member. They have been carrying out approximately 1.5 familial searches per week since 2004 (and some as early as 2002 at least, but they say they have no data prior to 2004). Each familial search can generate a long list of possibilities which is then narrowed down by using other intelligence such as geography, ethnicity and other ‘social assumptions’ such as the idea that people from criminal families are more likely to commit crime themselves. “