Politicians and observers who suspect that the official three-pronged investigation into the R43,8bn arms deal is designed to conceal rather than expose corruption need to reappraise their stance. The arrest and court appearance of former guerrilla commander Tony Yengeni on charges of corruption - and, alternatively, fraud, forgery and statutory perjury - is an important signal that the investigators will not be deterred by the political rank or allegiance of those against whom there is a prima facie case.

While Yengeni may be "small fry" in terms of his alleged offence - acceptance of a discount of nearly R168 000 on a luxury vehicle from DaimlerChrysler Aerospace SA - he is, or was until his arrest, an ANC notable of considerable weight.

His status as a regional commander in Umkhonto we Sizwe aside, he is a former chairman of the parliamentary defence committee and was at the time of his arrest last week the ANC's chief whip in the National Assembly. Under pressure from the ANC, he has since resigned this position.

At this stage, it is vitally important that the investigators complete their task in the same "without fear or favour" mode. For if the arms deal has been contaminated by corruption, it surely extends far beyond those foolish enough to accept favours from arms manufacturers. Defence Force Chief Siphiwe Nyanda was just such a recipient.

A process of corruption may have tarnished the primary contracts signed between government and the arms manufacturers given the go-ahead to supply the expensive weaponry. While government has repeatedly labelled the process of awarding primary contracts "fail-safe" against taint, such assurances should not deter the investigators. They must go where the evidence takes them.

As former ANC parliamentarian Andrew Feinstein has observed, the possibility exists that SA subcontractors with ANC connections may have extorted money or favours from the weapon-makers in return for using their influence to secure contracts for their benefactors.

If this turns out to be so, suspicions will pollute the political atmosphere for a long time yet. In that context, confirmation that former Defence Minister Joe Modise has been questioned by investigators is, like the arrest of Yengeni, an auspicious sign that, indeed, the probe will be far-reaching.

With acknowledgement to the Financial Mail.