City fire and building officials will search for new ways to target landlords who unlawfully subdivide their properties, said Mayor Michael Bloomberg in the wake of an April 25 Bronx fire that killed a family of three living in illegal subdivided housing.

The Department of Buildings gets about 20,000 annual calls about illegally converted apartments. Inspectors respond at least twice to every complaint and try to gain access to the building, but they are often turned away by tenants, or no one answers the door. If that happens, they must find evidence that the law is being broken and apply for a warrant to get inside.

At the Bronx building, inspectors had looked for evidence but couldn't find any, and no warrant was filed there, the agency said. The mayor said that constitutional protections against illegal search and seizure often present an insurmountable obstacle to city officials seeking to assure the safety of properties, especially because savvy owners don't put in extra mailboxes or doorbells where they're visible to the public. Two-thirds of city requests for access warrants are denied by the courts, City Council Speaker Christine Quinn said.