The suspicious white powder found in a letter sent to a Colorado campaign office for Republican presidential candidate John McCain is not anthrax or another lethal substance, officials determined Friday. The Colorado National Guard Civil Support Team completed its testing of the powder around 2 a.m. EDT (1800 GMT) Friday, Guard spokesman Rick Breitenfeldt said. Officials do not know what the powder is, but they determined it was not lethal. Thursday's scare had sent at least 19 people to hospitals for testing. Officials said the threatening letter was sent by an inmate at the Arapahoe Detention Center. Arapahoe County Sheriff's officials identified the inmate suspected of sending the letter as 39-year-old Marc Harold Ramsey, who has been incarcerated since September 2007 on investigation of felony menacing, harassment and second-degree assault on a peace officer. Ramsey may face federal felony charges for Thursday's incident, sheriff's officials said.