[UPDATE: 4/18/2013, 8:41 a.m.] An earlier version of this story misidentified the suspect based on initial information from police as Kenneth Curtis. The suspect’s name, who was arrested in association with mailing letters with Ricin to President Barack Obama and a U.S. Senator, is Paul Kevin Curtis of Tupelo, Miss.

Federal authorities have arrested a man in connection with two letters laced with ricin, one sent to President Obama and another mailed to Mississippi Sen. Roger Wicker. The suspect’s name was announced as Paul Kevin Curtis of Tupelo, Miss.

According to the Clarion Ledger, Curtis was arrested by the FBI on Wednesday after his connection to the letters, both sent a day earlier, was confirmed. So far, little is known about Curtis.

On Tuesday, Sen. Harry Reid announced that a letter containing trace amounts of the deadly poison ricin was sent to Senator Wicker. The letter had no return address and a postmark from Memphis. On Wednesday, it was announced that President Obama had received an extremely similar letter that also contained traces of ricin.

Federal officials concluded that the two ricin letters sent to Obama and Wicker were related because of the similar phrasing in both letters. Each ricin letter contained the phrase “to see a wrong and not expose it, is to become a silent partner to its continuance,” and ended with the signature “I’m KC and I approve this message.”

The Associated Press reports that neither ricin letter was delivered to its intended target. Since the 2001 anthrax attacks following 9/11, mail sent to the President and congressional offices has been routinely screened. The letter sent to Obama was screened in an off-site White House facility, while the letter intended for Wicker was screened at a facility in Prince George’s County, Md. 

According to NBC News, laboratory tests of the two letters tested positive for ricin, however, researchers were unsure about the potency. It is possible that Curtis did not fully synthesize the ricin toxin or that he inadvertently made a less potent and dangerous version.

Ricin is an extraordinarily deadly poison derived from castor beans. Typically, the poison is administered through injection or inhalation. According to a European Food Safety Authority report, a minuscule dose (less than 1/200th of an aspirin tablet) is poisonous enough to kill an able-bodied adult male within 36 hours. There is no known antidote.

Those opening a letter laced with ricin could be exposed to the poison in two ways. Simply touching the ricin residue is likely to do no more than cause a rash, but inhaling ricin particles in the air could easily lead to death. Nevertheless, despite ricin’s extreme toxicity, it has rarely been used as an effective poison. 

News that Obama and Sen. Wicker were sent a ricin letters came only one day after the city of Boston was rocked by a pair of explosions set off near the Boston Marathon finish line. The timing between the ricin letter and the Boston bombings bears an uncomfortable similarity to a string of anthrax attacks on government employees and media offices following the Sept. 11, 2001, attacks.

Only one week after the World Trade Center and Pentagon were attacked, two Democratic senators were sent letters containing deadly anthrax spores. Five people, including postal workers, were killed in the anthrax attacks.

The anthrax mailings are the primary reason why congressional mail is now screened in private facilities, a practice that allowed the ricin letters to be caught before they were delivered to Obama or Wicker.  

However, despite the ricin letters’ close timing to the Boston Marathon bombings, the FBI insists the two are not related. 

"The investigation into these letters remains ongoing, and more letters may still be received. There is no indication of a connection to the attack in Boston," the agency said Wednesday in a statement.