Investigators Try To Determine Who Sent Suspicious Package To U.S. Attorney

DENVER (CBS4) - Investigators are trying to find who sent a suspicious package to a downtown Denver office building. The FBI has joined the investigation.

Firefighters evacuated the building near 17th and Larimer and surrounded the area with crime tape.

The letter was sent to the U.S. Attorney's office and contained white powder.

Denver fire secured the site and determined that the powder was harmless protein powder. However, investigators are not revealing what was said in the letter.