The Anti-Defamation League has put out a press release declaring “Ricin a popular tool for domestic extremists.”

On Tuesday, letters possibly tainted with the highly toxic substance ricin were discovered in two separate mail facilities. One letter was addressed to President Obama and another was intended for Sen. Roger Wicker, R-Miss.

According to the ADL, which touts itself as “the nation’s premier civil rights/human relations agency,” domestic terrorists are attracted to ricin because it is easy to make.

“Many ricin incidents have stemmed from homegrown extremists, particularly right-wing extremists such as white supremacists and anti-government extremists,” the ADL declares in a statement released Wednesday.

Law enforcement officials told some senators they have a suspect but would not repeat that claim when asked by the press.

Neither letter reached the Capitol or the White House because mail for lawmakers and the president is screened off site.

The FBI is now involved in the investigation and the letters are being tested more thoroughly to see if the envelopes indeed contain ricin, which is so deadly that just a speck can kill if ingested.

Sometimes initial tests produce false positive results because the castor bean used to create ricin is also in some cases an ingredient in the paper-making process.

The ADL contends that manuals with ricin recipes, “written by or for right-wing extremists, ” are available at gun shows and “survivalist expos.”

In one manual, ADL says, called The Poisoner’s Handbook, the author suggests, "the poisoning of IRS workers by lacing tax return forms with ricin.”

In 2004, a ricin-laced letter was sent to a Senate office building but the sender was never caught.

The ADL also points out that some ricin incidents, “have been unrelated to a specific ideology.”