Det. Gus Villanueva declined Tuesday to discuss the nature of the threat against the talk show host, saying only that it came in an envelope sent from overseas.
Two people at CBS Television City, where "The Late Late Show" is filmed, were temporarily held in isolation after being exposed to the powder around 3 p.m. They were released after a hazardous materials team screened the powder and found it to be benign.
FBI spokeswoman Laura Eimiller said the agency was working with police to find out who sent the letter.
