The letter was delivered to the Dancing production offices located on the CBS lot in Los Angeles. The Los Angeles Fire Department and Police Department were notified, and the building was evacuated.
After initial testing, the white substance was determined to be talcum powder, a non-hazardous material. The letter is being sent to a regional lab for further testing, FBI spokeswoman Laura Eimiller told the AP.
The FBI declined to comment on who the letter was addressed to, People reports. "Just as in any case, we don't confirm the identity of a victim based on privacy and security concerns," Eimiller told the site.