NAACP employees were going through the mail Thursday at national headquarters in Baltimore when they found a strange-looking envelope. It bore no return address and had a Memphis, Tenn., postmark — just like letters to President Barack Obama and a Republican senator this week that tested positive for the deadly poison ricin.
Within minutes, the FBI ordered workers to evacuate, and emergency responders rushed to the scene.
It turned out to be a false alarm; the letter was a request for assistance. But the incident highlighted the jitters felt across the region this week, with courthouse evacuations and heightened security following the bomb attacks on the Boston Marathon and the poisoned letters in Washington.
"We're very conscious of everything going on," said Roger C. Vann, chief operating officer and chief of staff for NAACP.
Vann said similarities between the correspondence received at NAACP headquarters on Mount Hope Drive and the ricin letters that were intercepted before they could reach Obama and Sen. Roger Wicker of Mississippi aroused suspicions.
The civil rights organization quickly alerted authorities, who ordered all 100 employees to evacuate. The Baltimore City Fire Department's Technical Decontamination Unit and Special Operations Command trucks, a host of hazardous-materials workers and Baltimore police officers converged on the scene.
Within hours, they rolled back out. The FBI determined that the letter was "a nonhazard, nonsuspicious letter," agency spokesman Richard Wolf said.
Michael Greenberger, director of the University of Maryland Center for Health and Homeland Security, said false alarms are common after an attack, but that people should not feel embarrassed about reporting something that later turns out to be nothing.
"I'm a better-safe-than-sorry man," Greenberger said. "If someone in my law school building thought they saw something, I'm happy to walk out and be proved wrong."
FBI agents made an arrest Wednesday in the ricin mailings. Greenberger said the charges against Paul Kevin Curtis, 45, of Mississippi, will likely calm nerves.
"If this is, as it appears to be, a single person who has been arrested, this will die down," he said.
Officials said they are being especially cautious nonetheless.
Given the NAACP's history of being the focus of threats and acts of violence, Vann said, the organization constantly updates its system of safety measures and protocols. It followed them closely Thursday, he said.
"Everything worked like clockwork," he said.
Ryan O'Doherty, a spokesman for Baltimore Mayor Stephanie Rawlings-Blake, said the city boosted its mail security this week in response to the ricin letter in D.C. He declined to provide details, to avoid compromising the protections.
Raquel M. Guillory, a spokeswoman for Gov. Martin O'Malley, said Maryland has "coordinated throughout state government to ensure that protective measures are in place and up to date."
O'Malley and another state official were targeted in 2011 with mailed incendiary devices, prompting a temporary shutdown of government mailrooms. No one has been arrested; U.S. Postal Inspector Frank Schissler said Thursday that that investigation is continuing.
Schissler said the Postal Service checks mail at its processing facilities. Many government agencies add their own scanning operations.
"I can't go into the details of what the system does or does not detect, because that kind of gives away what we're trying to prevent," he said.
Other threats, which proved to be hoaxes, have come in across the region.