More anthrax hoax letters sent to lawmakers

Several letters filled with suspicious powder were recently sent to more Senate state offices, though the Senate's top law enforcement official said the messages were tested and found to be harmless.

The latest incidents followed a string of mailings to congressional offices and media outlets that also proved to be harmless, according to CBS News.

"It is clear that the person sending these letters is organized and committed, and the potential to do harm remains very real," Sergeant-at-Arms Terrance Gainer said, CBS News reports. "Although all letters received thus far have proved harmless, it is essential that we treat every piece of suspicious mail as if it may, in fact, be harmful."

Last week, three state and home district offices received threatening letters, including a district office of House Speaker John Boehner (R-Ohio).

The sender wrote that he wants an end to "corporate money and lobbying" and calls for a new constitutional convention. He said that he would place a pathogen randomly into the letters and that he was unsure of who would actually receive something dangerous.

"So far, none of the letters have contained a hazardous substance," FBI Special Agent Jason Pack said, CBS News reports. "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."