The allegations against S.C. House Speaker Bobby Harrell certainly deserve careful scrutiny. But it is highly questionable whether state Attorney General Alan Wilson should be conducting the investigation.

The State Law Enforcement Division (SLED) assigned agents last week to begin investigating Harrell, one of the state’s most powerful elected figures. The official complaints against the Charleston Republican were forwarded to SLED two weeks ago by Wilson.

Harrell’s chief accuser is Ashley Landess, president of the S.C. Policy Council, a libertarian think tank. The agency questions the legality of Harrell reimbursing himself $280,000 from his campaign account since 2008 for, among other things, using his personal plane while traveling on state business.

When the complaint came to light, Harrell returned about $23,000 to his campaign for expenses for which he could not supply receipts.

Harrell also has been accused of appointing his brother to the Judicial Merit Selection Commission, a committee that screens and nominates judicial candidates, posing a potential conflict of interest for Harrell. Harrell also has been accused of using his position to apply pressure to the S.C. Pharmacy Board and the S.C. Department of Labor, Licensing and Regulation to help his pharmaceutical business.

Last month, the political watchdog group Common Cause called on Harrell to step down. But the group also has questions about Wilson’s involvement in the investigation.

Wilson, the state’s top prosecutor, is under scrutiny for not reporting at least 10 donations on campaign filings following his 2010 election win. Among other donations, the first-term Republican from Lexington sought $3,500 from Harrell for the attorney general’s inaugural gala.

Wilson also received a $3,500 campaign contribution from the Palmetto Leadership Council, which has ties to Harrell.

While Wilson claims the contributions “in no way conflicted in our responsibility to uphold the law,” his campaign returned $7,000 in contributions tied to Harrell. “Appearance does matter,” Wilson added.

Harrell asserts that under an opinion issued by the House Ethics Committee in 1999, use of campaign money for nonprofit events such as the gala is permitted. But the Ethics Commission also has ruled that candidates cannot share contributions.

At best, it appears to be a legal gray area. Which begs the question why two of the state’s highest ranking politicians would take the risk of comingling contributions.

Wilson has said he has no intention of removing himself from the Harrell probe. Under the circumstances, however, it would appear he has little choice but to recuse himself.

Harrell’s use of campaign funds deserves a full investigation. Wilson might be guilty only of not knowing the rules barring exchange of campaign money between candidates, but that is damning in itself for the state’s top lawyer.

This controversy reflects both the unhealthy influence of big money in South Carolina politics and the lack of ethical oversight. That makes it all the more important that state lawmakers rewrite ethics rules and require more disclosure of how campaign contributions are used.

They also need to give the state ethics commission enough authority and independence to hear and investigate complaints, and punish lawmakers who break the law.