The killing last week of a dozen Iraqi civilians by a private American security firm and the Iraqi reaction underscored why thousands of contractors will remain in Iraq but also why U.S. officials must do a better job of overseeing them.

Guards working for Blackwater USA, a private security contractor, are accused of opening fire on a crowd in Baghdad on Sept. 16, killing at least 11 civilians. Company officials say the guards were protecting a motorcade and fired shots after a car bomb exploded nearby.

Shortly after the incident, Iraqi Prime Minster Nouri al-Maliki threatened to expel the company from Iraq.

A week later, a spokesman for the Iraqi security forces said this was not possible because it would cause a “security vacuum,” because military personnel would have to be brought in to guard foreign embassies in Baghdad. Taking soldiers away from areas where they are battling insurgents would cause “a big imbalance in the security situation,” Tahseen Sheikhly said at a news conference on Sunday.

By some estimates, the number of private contractors in Iraq equals the number of U.S. military personnel there. Since private contractors are in Iraq to stay, better oversight of their activities is necessary. Committees in Iraq and Washington have launched reviews of the Blackwater incident and are to recommend improvements. A 16-member commission in Iraq will look at tighter regulation. Under an order put in place in 2004 by the Coalition Provisional Authority, U.S. contractors are not subject to Iraqi law. In Washington, the State Department will examine how U.S. officials are protected in Iraq.

Like the two committees, private contractors fall into two separate groups in Iraq. One supplements military operations, such as staffing U.S. bases and transporting supplies, often working alongside Iraqis. This group is under the direction of the Department of Defense. Congress requires that these contractors abide by the Uniform Code of Military Justice.

Contractors that provide security services are overseen by the State Department with an emphasis on protecting high-ranking personnel. Blackwater is one of three companies providing these services in Iraq. Because protection, not cooperation with local officials is their mandate, this group is seen as heavy-handed and is viewed more suspiciously by Iraqis.

The State Department has its own set of rules for security contractors, but after repeated requests The Washington Post, which did an extensive review of the situation, was unable to find out what those rules are.

This would be a good place for the special inspector general for Iraq to begin a review, as suggested by Sen. Susan Collins, who authored legislation creating and maintaining this office. The IG should find out what the State Department’s standards are and if they are adequate or if they should be closer to the Pentagon rules. A further step would be to assure that the rules are being followed.

It is in the interests of the Iraqi and U.S. government to assure that contractors, who are an essential part of the ongoing security and reconstruction work, are held to high standards.