DURHAM, N.C. — The chief deputy attorney general blames five construction companies for the mold that shut down two dorms at North Carolina Central University, and he threatens to sue if they do not reimburse the state for the cleanup.

Last August, inspectors found toxic black mold in both dorms, forcing hundreds of students into area hotels. The dorms were only 4 years old.

The state has since spent millions of dollars cleaning out the mold. The UNC Board of Governors asked the attorney general's office to look into what went wrong and who was to blame.

Investigators determined the mold and moisture damage resulted from a combination of poor design, construction methods and materials.

All five companies got letters from the attorney general's office Thursday. Among them is the architectural firm owned by former Charlotte mayor and former U.S. Senate candidate Harvey Gantt. In an effort to avoid a lawsuit, the attorney general's office is offering to meet with all of the companies next week to talk about a possible settlement.

Officials estimate the total costs spent on the mold problem will exceed $9 million. Next week, both dorms are slated to officially reopen for the first time since they were shut down last summer.