The murder of Collette Aram took place before DNA testing was available. Hutchinson was interviewed as part of the original investigation. If the investigation were taking place today Hutchinson would be asked for a DNA sample and there would be no need to call on a database containing DNA from his relatives.
The number of old unsolved cases like this one, where DNA evidence could still provide a clue, is finite and must be few in number and dwindling. These cases hardly provide a justification for the expense of maintaining a huge DNA database, let alone the interference with civil liberties.
It always seems to be this kind of case that results in calls for a DNA database, but despite tragic cases like Collette Aram's, Britain is an extraordinarily safe place. If you do become one of the few hundred people murdered each year it is most likely to be by someone close to you, who is easily identified. Despite the emphasis put on this type of crime by the press, you are probably more likely to win the National Lottery jackpot than be murdered by a stranger, which in itself makes the Hutchinson case a bad argument for a national database.