The FBI arrested a Corinth, Miss. resident yesterday in connection with a series of letters tainted with the deadly poison ricin that were caught this week at White House and U.S. Capitol mail screening facilities.

Secret Service found letter mailed to President Obama laced with “suspicious substance,” more suspicious letters sent to senators, and now a Senate office building is on lockdown.

The Capitol Building yesterday (Getty Images) A letter, addressed to Mississippi Senator Roger Wicker’s office, tested positive for the toxic poison ricin. According to the Washington Post, the letter was found this morning “at an off-site location where congressional mail has been screened since anthrax-laced letters were sent to Capitol Hill in 2001.” The mail facility is located in Washington, and a law enforcement told CNN said that the envelope tested positive in a…