Pressure is building on the prosecution to investigate growing suspicions of illegal fundraising by aides to President Lee Myung-bak during the 2007 presidential race.

Opening a probe into presidential campaign finance must be something the prosecution wants to avoid as much as possible as it could involve the incumbent president.

But it is its duty to launch an investigation as circumstantial evidence strongly suggests Lee’s campaign raised funds illegally. If the prosecution shies away from taking action on this matter, its political independence and impartiality, which is already in doubt, will be further undermined.

Suspicions of illegal campaign funding were reignited by Choi See-joong, a former head of the Korea Communications Commission who is known to be one of Lee’s political mentors.

The former Gallup Korea chairman was arrested in April on charges of taking 800 million won in bribes from Pi City, a real estate developer, between July 2006 and February 2008.

During a court hearing this week, Choi argued that 600 million won of the money was not a bribe since the property developer gave it “without attaching any strings.” All it wanted, he claimed, was to help with Lee’s campaign.

In April, Choi said he used the “donations” to cover the cost of conducting opinion polls. But he soon retracted his words, saying he used the funds for private purposes. At the hearing, he switched his stance again.

The flip-flops are understandable. If Choi is convicted of taking bribes for influence peddling, as charged by the prosecution, he is subject to a maximum sentence of five years in prison.

But if he used the money not for personal purposes but for electioneering, he will be punished under the Political Fund Act and face a maximum prison sentence of three years. The verdict could be even lighter as the statute of limitations on illegal political funding cases is five years.

As Choi reversed his testimony and claimed to have used the illicit Pi City funds to campaign for Lee, the prosecution needs to trace the whereabouts of the money.

If Choi did use the illegal funds to finance Lee’s campaigning, it would contradict the president’s remark last September. At the time Lee declared with confidence that his government was “morally perfect.”

What he meant was that his campaign did not raise or spend a penny in an illegal way.

Yet suspicions about campaign financing irregularities have since surfaced as Lee’s close confidants began to be arrested one after another in connection with the ongoing savings bank scandal.

Lee’s elder brother, Lee Sang-deuk, was arrested for receiving 300 million won from the chairman of Solomon Savings Bank before the December 2007 presidential election.

Although the former six-term lawmaker was indicted for bribery charges, the money he received is believed to have been spent for his younger brother’s presidential campaign.

The president’s brother was also suspected of having received 300 million won in “congratulation money” from Ra Eung-chan, a former Shinhan Bank chairman, two months after Lee’s election victory.

The prosecution should start an investigation without further hesitation as the statute of limitations will soon expire. We believe there is enough circumstantial evidence to justify a full-fledged investigation.

Prosecution action on the matter is all the more necessary as the December presidential election is just months away. An investigation into Lee’s campaign financing will serve as a timely warning for all presidential hopefuls.

We do not suspect that the president himself was involved in any illegal funding schemes. But if any of his aides are found to have been involved, Lee should bear responsibility, at least morally. He already owes an apology to the public for the indictment of his brother and other confidants.

In recent years, the prosecution has been widely discredited due to its failure to maintain independence in handling politically sensitive cases. It should not miss out on a good opportunity to redeem itself. Without restoring authority, it will not be able to enforce the law in a just and equitable manner.