This post has been updated.
Authorities determined that a suspicious white, powdery substance sent in a letter to Sen. Pat Toomey's Center City office on the 17th floor of 8 Penn Center was cornstarch, police said late Thursday afternoon.
Homeland Security, fire and haz-mat officials were on scene investigating the incident around 3 p.m., and about an hour later, the determination that the substance was harmless was made, said Officer Tayna Little, a police spokeswoman.
An intern had opened the letter containing the white powder, Little said.
The envelope and substance were placed in an empty office while authorities investigated the incident.
District offices of other members of Congress, including House Speaker John Boehner, have also reportedly received letters containing a white, powdery substance recently. That substance, according to reports, proved to be harmless upon testing.