From the front page of spaceflight.nasa.gov:

NASA Asks For Help With Columbia Investigation

Anyone who discovers debris from the accident or who has film or video evidence that may be of value to the investigation team is urged to use these contacts. Please avoid contact with any debris, because it may be hazardous as a result of toxic propellants aboard the Shuttle.

Telephone reports should be directed to the following number: 281/483-3388

Text reports and images should be e-mailed to: nasamitimages@jsc.nasa.gov

The e-mail address is: columbiaimages@nasa.gov

All debris is United States Government property and is critical to the investigation of the shuttle accident. Any and all debris from the accident is to be left alone and reported to government authorities. Unauthorized persons found in possession of accident debris will be prosecuted to the full extent of the law.