The FBI has identified a Mississippi man suspected of mailing letters containing poisonous ricin as 45-year-old Paul Kevin Curtis.

US Postal Service mailbox in Ocean County (Jason Allentoff, Townsquare Media NJ)

FBI Special Agent in Charge Daniel McMullen said Curtis was arrested Wednesday afternoon at his apartment in Corinth, near the Tennessee state line about 100 miles east of Memphis.

Authorities still waited for definitive tests on the letters sent to President Barack Obama and Sen. Roger Wicker, R-Miss.

An FBI intelligence bulletin obtained by The Associated Press said those two letters were postmarked Memphis, Tenn.

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Suspect In Mind

Sen. Claire McCaskill, D-Mo., said that police had a suspect in mind in the Wicker mailing, someone who "writes a lot of letters to members." She made the comment Tuesday as she emerged from a briefing by law enforcement on the Boston bombing. Authorities declined to comment on a possible suspect.

Obama's press secretary, Jay Carney, said mail sent to the White House is screened at a remote site for the safety of the recipients and the general public. He declined to comment on the significance of the preliminary ricin result, referring questions to the FBI.

All three packages in the Capitol complex turned out to be safe, Capitol police spokeswoman Makema Turner said late Wednesday.


What is Ricin ?

Ricin is a poison found in castor beans. A highly toxic version using Ricin can be manufactured into a powder, mist or pellet form or dissolved in water.

"It would take a deliberate act to make ricin and use it to poison people," according to the Center for Disease Control's Facts on Ricin.

Depending on the dosage and method of exposure, death from Ricin poisoning is likely between 36 to 72 hours from time of exposure.

 How Does Ricin Work?

Ricin works by invading cells, then preventing the body's cells from creating the proteins it needs to survive.

There is no antidote for Ricin according to the CDC, and treatment includes attempting to minimize the effects of the poisoning.

CDC's Signs of Ricin Exposure:

If you inhale Ricin: Respiratory distress, fever, cough, nausea, heavy sweating, low blood pressure, respiratory failure, then death.

If you ingest Ricin: Vomiting, bloody diarrhea, severe dehydration, low blood pressure, seizures, blood in the urine, organ shutdown, death.

If you get Ricin on skin or in eyes: Contact with the skin could cause redness, pain of the skin or eyes.

The Associated Press contributed to this story