Officials have determined that the suspicious white powder mailed to John McCain’s Denver campaign office along with a death threat is not anthrax. Experts say they’re not certain what the substance is, but they’re sure it’s not harmful.

The Secret Service has identified the person suspected of sending the Denver letter. The suspect, Marc Harold Ramsey, is an inmate at the Arapahoe Detention Center who has been incarcerated since September of 2007.

Ironically, the crimes that landed Ramsey in prison to begin with are felony menacing, harrasment, and second-degree assault on a police officer. Ramsey will likely now face federal felony charges relating to the fake anthrax letter and death threat.

John McCain’s office in Denver received an envelope containing a death threat and some quantity of white powder this afternoon.

John McCain’s campaign office in Denver, Colorado, has received a letter containing a threat and “an amount of white powder in it,” a McCain campaign spokesman told CBS News’ Michelle Levi.

“We immediately notified local and federal law enforcement agencies and are looking to cooperate with them,” McCain spokesman Jeff Sadosky said.

The city of Denver is at a heightened security level, as the Secret Service and other officials prepare for the Democratic National Convention, which is set to begin on Monday.