Source: Letter to Obama positive for ricin

A menacing letter sent to President Barack Obama has tested positive for ricin, a law enforcement source said Friday.

The letter had a Shreveport, La., postmark and similar wording to ones sent to Mayor Michael Bloomberg and his gun-control advocacy group, which also were tainted with ricin, the source said. All three letters were postmarked May 20, federal officials said.

Authorities, who think all three letters were sent by the same person, questioned a Texas man in the case Thursday. But Friday authorities were proceeding with caution with this man because they became unsure of the credibility of his wife, who told authorities about him, the source said.

Authorities are investigating any possible connections to other ricin-tainted letters, the source said.

Federal authorities in Spokane, Wash., are investigating whether a man indicted there on charges he sent ricin-laced letters in mid-April to Obama, a federal judge, the CIA, an Air Force base and a post office is connected with the Shreveport letters, the source said.

In the Spokane case, Matthew Ryan Buquet, 38, was charged May 22 with a one-count grand jury indictment for mailing threatening communications, the FBI said. The letters he's suspected of mailing were addressed in handwritten red ink, according to the FBI.

The key ingredient in ricin -- castor beans -- is easy to find. Crude instructions for extracting the lethal poison in them can be found on the Internet. And it doesn't require a chemistry degree or sophisticated lab equipment.

Ricin has been sent to officials sporadically over the years, but experts say there seems to be a recent uptick and that copycat attacks -- made possible by the relative ease of extracting the poison -- may be the reason.

"I can absolutely promise you that when these kinds of things happen, we're going to have copycats. We expect them. We prepare for them. And we catch them," said Murray Cohen, founder of the Atlanta-based Frontline Foundation, which trains workers how to respond to bioterrorism and epidemics.

If inhaled, ricin can cause respiratory failure, among other symptoms. If swallowed, it can shut down the liver and other organs, resulting in death. The amount of ricin that can fit on the head of a pin is said to be enough to kill an adult if properly prepared. No antidote is available, though researchers are trying to develop one.

With AP