The police department said Thursday that it is investigating about a dozen officers suspected of looting during the lawlessness that engulfed the city after Hurricane Katrina.

News reports in the aftermath of the storm put officers at the scene of some of the heaviest looting, at the Wal-Mart in the Lower Garden District. Some witnesses, including a Times-Picayune reporter, said police were taking items from shelves.

"Out of 1,750 officers, we're looking into the possibility that maybe 12 officers were involved in misconduct," police spokesman Marlon Defillo said.

He rejected the use of the term "looting" and said authorities were investigating "the possibility of appropriation of nonessential items during the height of Katrina, from businesses."

Earlier this week, the city's police superintendent, Eddie Compass, resigned after weeks of criticism about the department's conduct during Katrina and its aftermath. On the same day, the department said about 250 police officers could face discipline for leaving their post without permission during the crisis.

Meanwhile, business owners started streaming back into newly reopened sections of the city Thursday morning at Mayor C. Ray Nagin's invitation. Some vowed to rebuild, and some said they were pulling out.

The areas thrown open to business owners were the French Quarter, the Central Business District and the Uptown section, which includes the Garden District, a leafy neighborhood of antebellum and Victorian mansions. The neighborhoods escaped major flooding during Katrina.

Under the mayor's plan, residents of those neighborhoods will be allowed to return on Friday, a move that could bring back about one-third of the city's half-million inhabitants.

Acting Police Superintendent Warren Riley, right, tells reporters about the looting investigation.