AP:

CENTENNIAL, Colo. - Authorities say a threatening letter containing an unidentified white powder was sent to a John McCain campaign office in the Denver suburb of Centennial, and a similar letter was sent to a McCain office in Manchester, N.H.A hazardous materials team was trying to determine if the powder found in Colorado is harmful.

It wasn't immediately known if the New Hampshire letter also contained a powder, said Jeff Sadosky, a spokesman with McCain's national campaign office in Arlington, Va. Read on...

There are few details at this time, we'll keep an eye on the story.

UPDATE:

Federal law enforcement sources tell NBC News that a threatening hand-written letter that sparked an evacuation of Sen. John McCain's Centennial office was sent by a person being held in the Arapahoe County Jail.

NBC News says the person is a prolific letter writer who was already in the jail.

Sources also tell NBC that there is no link between the Colorado letter and another threatening letter that appeared on Thursday at McCain's office in Manchester, New Hampshire. That letter had a return address from Denver, but investigators do not believe the two incidents are connected. Read on...