Last year, federal and local authorities busted a Chinese man for operating a chain of Twin Cities-area brothels using illegal immigrants as prostitutes. Last week, he was convicted, sentenced and now faces possible deportation.

Prosecuting a sex-trafficking kingpin is an important victory in the battle against brothels, which are often dens of modern-day slavery. And officials involved in the arrest say several similar investigations are underway in Minnesota.

Still, much remains to be done to increase arrests and make real progress in fighting human trafficking. More effort and resources must be used to identify situations in which women or children are exploited, get them help rather than punishment, and make sure that male operators and customers are also held responsible.

According to a needs assessment study released this week by Minneapolis-based Advocates for Human Rights, disparities persist in sex-trafficking enforcement. The report was commissioned by the state Human Trafficking Task Force, a statewide group created by the Legislature to collect trafficking data.

After conducting 175 interviews with police, prosecutors, service providers and others, the study found numerous incidents of "selective and uneven'' treatment of customers. "In one state jurisdiction, 284 misdemeanor prostitution-related cases were submitted to a prosecutor, but only 30 of them involved patrons.''

Changing that ratio is among two dozen recommendations in the report. Other reasonable suggestions include improving public awareness, increasing resources for victims, and providing more training for police, prosecutors and others to help them identify and assist those trapped in sexual servitude.

The report also calls for some sensible modifications to both state and federal laws to make them more consistent. Under federal rules, officials must prove that "force, fraud or coercion'' was used to get someone into prostitution. By contrast, Minnesota law recognizes that a "person can never consent to being sexually exploited, and considers individuals who have been prostituted by others as trafficking victims,'' the report states.

At the federal level, Congress is currently debating language for the reauthorization of the Federal Trafficking and Victims Protection Act of 2000. Prosecutors have had difficulty making cases against pimps and traffickers because the "force'' standard can be tough to prove.

The House version of the reauthorization would help prosecutors by adding "persuade, induce or entice'' to the criteria list. That would make it somewhat easier to pursue domestic cases where local runaways, poor or otherwise vulnerable people become swept up in the sex trade. The Senate should also adopt those provisions.

Unfortunately, because of the huge demand and large amounts of money, there's plenty of incentive for underground pimps to set up shop. Even law enforcement officials admit that when they shut down one operation, others pop up in its place.

In the face of that persistence, it's important to keep the pressure on to convict and punish more masterminds and customers. And in the process, there should be more protection, understanding and support for the victims of sex trafficking.