The FBI has identified a Mississippi man suspected of mailing letters containing poisonous ricin as 45-year-old Paul Kevin Curtis. Curtis was arrested Wednesday evening near Memphis. (Courtesy of Washington Post)

[The Washington Post]

The FBI has identified a Mississippi man suspected of mailing letters containing poisonous ricin as 45-year-old Paul Kevin Curtis. Curtis was arrested Wednesday evening near Memphis. (Courtesy of Washington Post)
Fire crews arrive at the unmarked postal building by the Beltway every few days, donning protective rubber suits and carrying away suspicious letters addressed to members of Congress. At a similarly secret building in the District, agents set aside letters once or twice a week to the president containing powder or other cause for concern. For years — ever since the anthrax attacks of 2001 — nearly every one has proved harmless.But alarms sounded in both buildings this week, and the threats appeared real: A grainy substance tested positive for the lethal toxin ricin in letters addressed to President Obama and a quiet senator from Mississippi.

By Wednesday night, authorities had arrested Paul Kevin Curtis of Corinth, Miss., as a suspect in the ricin mailings, the FBI said in a statement. Curtis also sent a third letter to a Mississippi justice official, the FBI said. He is well known to law enforcement as a frequent letter-writer to lawmakers, two officials said.