(CBS/AP) Several more Senate state offices have received "threatening mail containing a suspicious powdery substance," though the messages were found to be harmless, the Senate's top law enforcement officer told CBS News Thursday.
The latest incidents follow a string of similar mailings to congressional offices outside Washington and media organizations that also proved to be harmless, according to authorities.
Still, Sergeant-at-Arms Terrance Gainer said "it is clear that the person sending these letters is organized and committed, and the potential to do harm remains very real."
On Wednesday, letters were sent to three state and home district offices, including a district office of House Speaker John Boehner, R-Ohio, according to his spokesman.
Letters were also sent to several media organizations, including Comedy Central comedians Jon Steward and Stephen Colbert.
The author told the comedians he would send letters to all 100 senators and 10 percent of them would contain "lethal pathogens," an official told CBS News.
The sender wants an "end to corporate money and 'lobbying,'" an end to corporate "personhood" and a new constitutional convention.
The author also said he "randomized" which letters would contain the pathogen and even he did not know who would get which letter, the official said.
"So far, none of the letters have contained a hazardous substance," FBI Special Agent Jason Pack said Wednesday. "We are working with those law enforcement agencies affected to determine if the mailings are related. We take these matters seriously and will investigate fully."
The letters delivered Wednesday bore a return address from "The MIB" and were postmarked Portland, Ore.
The Portland return address on the letters appears to be phony. The combination of the address given — 2413 NW Burnside, ZIP code 97209 — does not exist.
The threats raised memories of post-9/11 incidents that rattled Washington. In mid-November 2001, authorities closed two Senate office buildings after anthrax attacks on Congress. Those attacks came after four people — two postal workers in Washington, a New York City hospital worker and a Florida photo editor — died from exposure to anthrax.
Also at that time, an unopened envelope sent to Sen. Patrick Leahy, D-Vt., resembled a letter mailed the previous month to then-Senate Majority Leader Tom Daschle, D-S.D. The Leahy letter was discovered in the 280 barrels of congressional mail quarantined after a Daschle employee opened a powder-filled envelope.