A second letter sent to a McCain campaign office in New Hampshire initially was reported to contain threatening language and white powder. Authorities said that was a false alarm and there was no powder in that envelope.
At least 19 people were examined at hospitals or were quarantined outside the Colorado office while authorities tried to determine whether the powder was hazardous. Everyone was sent home by late Thursday, said Arapahoe County Sheriff Grayson Robinson. He said the substance was not hazardous and not lethal, but that it will take days to determine what it was.
Andy Lyon of Parker South Metro Fire Rescue Authority said the return address on the envelope listed the Arapahoe Detention Center and the name of an inmate.
Sheriff's officials said the inmate suspected of sending the letter is Marc Harold Ramsey, 39, 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.
Lyon said the first line of the letter used threatening language. He refused to give any details.
Malcolm Wiley, a Secret Service spokesman in Colorado, said there was no powder in the New Hampshire envelope. He said he did not know about the content of the letter, which had a Denver return address. That alarmed staffers in Manchester, who had heard about the Colorado incident.
Jim Barnett, McCain's New England campaign manager, said it's unusual for the New Hampshire office to get a letter from Denver.
"That was really the only suspicious thing about the letter, and our national headquarters advised, out of an abundance of caution for our staff and volunteers, that we have the authorities check it out," he said. "We did and it was deemed safe."
Barnett said the letter contained "kind advice" to McCain. According to Manchester Police, the New Hampshire letter contained information about the support McCain would receive from Polish-American voters if he chose former New York Gov. George Pataki as his running mate.
A government official familiar with the investigation said authorities believe the Denver letter was a hoax because it appeared to have been sent from a jail.
Both the New Hampshire and Colorado offices were evacuated.
Bruce Williamson of the Arapahoe County Sheriff's Department said authorities took the incident "very seriously" because the Democratic National Convention begins Monday in Denver. McCain is the presumed GOP candidate.