The decision of the Korean businesswoman who had laid a complaint against disgraced MP Richard Worth to withdraw her allegation must have caused some consternation to police working on the case. Thus deprived of their star witness they can hardly be blamed if they drop the matter, rather than waste further time with it.

Worth will doubtless be highly relieved. He professed confidence that when the facts were established he would be cleared, but it would be surprising indeed if he maintained his previous enthusiasm for publishing the truth of the matter. He can (and doubtless will) now maintain his silence, secure in the knowledge that, having not been found guilty, he may enjoy the perpetual presumption of innocence.

But that is true only in a technical sense. The police must have assessed the businesswoman's complaint as having some merit, or they would not have investigated it for a month. And in the silence, whether Worth likes it or not, the stain of the affair continues to get darker; it does not fade.

The silence of the Prime Minister, John Key, is more problematic still. At first declining to comment because it was the subject of a police investigation, he later said he had "washed his hands" of Worth (who had resigned as a minister and, later, as an MP) and had moved on. But it is not satisfactory for the matter to be left hanging. Cabinet protocol may not require Key to disclose why he lost confidence in his minister and the caucus lost confidence in its colleague. But justice requires that we be told.

This is not simply a question of prurient gossip. The businesswoman's reported statement that Worth had lost his place in the Parliament "and that is enough" (taken together with Labour's having called off its attack over separate allegations once the MP was gone) leaves open the possibility that the object was always to hound him from office. In the interests of transparency of the executive, the matter must be brought to a tidy close - and not simply left to fade away.