Seven weeks after the discovery of ricin on Capitol Hill prompted the mass collection of unopened mail from House and Senate offices, the Capitol Police have approved the redistribution of thousands of letters and other items beginning today.

According to a “Dear Colleague” letter issued by House Chief Administrative Officer Jay Eagen, the police released mail to House Postal Operations for distribution after it had been tested for toxins under new mail security protocols.

According to a spokeswoman for the Senate Sergeant-at-Arms office, as mail has been received back from the investigators it has been screened and redelivered to offices. “The mail that was collected on the Senate side has actually been redistributed all along,” she said.

The Capitol Police, with the assistance of the Marines and Coast Guard, collected unopened mail from all House and Senate offices after the Feb. 2 discovery of the toxin ricin in Senate Majority Leader Bill Frist’s (R-Tenn.) personal office.

“The condition of the mail may vary depending upon the treatment it received while being investigated,” the March 19 letter states. “If you do not wish to receive this mail, you may refuse delivery and the mail will be destroyed accordingly.”

Mail delivery resumed in both chambers in mid-February after new screening procedures were put in place; mail is now opened in off-site facilities, then tested and resealed before being delivered to its Congressional recipient.

In the meantime, Capitol Police and FBI officials are continuing an investigation into the source of the ricin, after testing failed to locate a “hot letter,” or item containing traces of the toxin, which is made from castor beans.

“We’ve exhausted the possibility of finding a letter,” Gainer acknowledged in an interview earlier this month. Without another letter or additional evidence, it appears “there is no break on the horizon,” he added.

FBI investigators — who are also looking into two apparently unrelated ricin-tainted letters discovered in October 2003, one addressed to the White House and another to the Transportation Department — are now handling the bulk of the investigation, Gainer said.

“The focus has shifted out of the District for now,” he added.

An FBI spokeswoman confirmed earlier this month that investigators do not believe the ricin found in Frist’s office is not a false positive created by pulp used to make some envelopes, as had been suggested in media reports.