Kenneth Curtis of Tupelo, Miss., to be exact. Letters that tested positive for ricin and were addressed to Sen Roger Wicker and Sen. Barack Obama were both reportedly signed, “I”m KC and I approve this message.” Update: The AP has the FBI naming the suspect Paul Kevin Curtis of Corinth, Miss. Early reports are always, of course, subject to a grain of salt, and the AP hasn’t been terribly reliable today, but those are the two IDs floating around.

Federal sources have confirmed to The Clarion-Ledger that Kenneth Curtis of Tupelo has been arrested in connection with letters laced with ricin that were sent to Sen. Roger Wicker and President Barack Obama.

Federal authorities were in Tupelo on Wednesday investigating the letters. Both letters were signed: “I am KC and I approve this message.”

Agents with the Secret Service and the FBI used the Lee County Sheriff’s Department as a staging area for their investigation. Lee County Sheriff Jim Johnson confirmed an investigation, but would not comment on the nature of the investigation.

Wicker has an office in Tupelo, and has been assigned a protective detail. I’m glad to see the mail-screening process implemented post-Anthrax incidents apparently working as intended:

An FBI bulletin obtained by Fox News said the letter sent to Obama is still being screened, though it initially tested positive.

The bulletin said both letters included the phrase: “To see a wrong and not expose it, is to become a silent partner to its continuance.”

Both were signed, “I am KC and I approve this message.”

The envelopes had Tennessee postmarks, but no return address.

Sources say officials are familiar with the person believed to have sent the letter as the person has sent other letters before.

The suspect sounds like he may be a cornucopia of crazy, but we’ll see as more information comes out. The initial ricin test can be a false positive, and the Washington Post notes, “More elaborate testing to verify the presence of the poison — using fluorescent antibodies, chromatography and searching for DNA — can take 24 to 48 hours, one law enforcement official said.”

A peek inside the screening process, also from the Post:

The letter to Obama was intercepted Tuesday at a Secret Service-run mail sorting facility in Anacostia, according to law enforcement officials.

The FBI said in a statement Wednesday that the letter contained “a granular substance that preliminarily tested positive for ricin.” Authorities did not say when or where the letter was postmarked.

The other letter, to Wicker, was uncovered Tuesday at a Prince George’s County sorting facility where congressional mail has been screened since anthrax-laced letters were sent to Capitol Hill in 2001. The letter to Wicker was postmarked from Memphis and contained no return address and no “outwardly suspicious” markings, Senate Sergeant at Arms Terrance Gainer wrote to senators in an e-mail.

Both letters were signed, “I am KC and I approved this message,” according to NBC News.

The two letters were transferred to a secondary testing facility in Maryland, according to the law enforcement officials, who spoke on the condition of anonymity because the investigation was ongoing.

A glimpse of the investigation came outside a low-slung, white-and-green postal warehouse north of FedEx Field, where county fire crews helped emergency workers suit up in white-and-yellow hazmat suits before trudging inside a yellow tent. Two black SUVs and a car bearing the insignia of the FBI Joint Terrorism Task Force sat behind the building.