Multiple U.S. officials told The Associated Press that former Army scientist Bruce Ivins was long obsessed with the sorority Kappa Kappa Gamma, going back as far as his own college days at the University of Cincinnati.
The officials all spoke on condition of anonymity because they were not authorized to discuss the case publicly.
The bizarre link to the sorority may indirectly explain one of the biggest mysteries in the case: why the anthrax was mailed from Princeton, N.J., 195 miles from the Army biological weapons lab the anthrax is believed to have been smuggled out of.
An adviser to the Kappa Kappa Gamma chapter at Princeton University confirmed she was interviewed by the FBI in connection with the case.
U.S. officials said e-mails or other documents detail Ivins' long-standing fixation on the sorority. His former therapist has said Ivins plotted revenge against those who have slighted him, particularly women. There is nothing to indicate, however, he was focused on any one sorority member or other Princeton student, the officials said.
Despite the connection between Ivins and the sorority, authorities acknowledge they cannot place the scientist in Princeton the day the anthrax was mailed. That remains a hole in the government's case. Had Ivins not killed himself last week, authorities would have argued he could have made the seven-hour round trip to Princeton after work.
Investigators know the pre-stamped envelopes, which delivered the deadly powder, were purchased at a Frederick, Md. post office near Ivins home - but it's unclear if investigators can connect Ivins to the envelopes, reports CBS News correspondent Bob Orr.
Ivins' attorney, Paul F. Kemp, did not immediately respond to a message seeking comment Monday but has asserted his client's innocence and said he would have been vindicated in court.
Katherine Breckinridge Graham, a Kappa alumna who serves as an adviser to the sorority's Princeton chapter, said Monday she was interviewed by FBI agents "over the last couple of years" about the case. She said she could not provide any details about the interview because she signed an FBI nondisclosure form.
However, Graham said there was nothing to indicate that any of the sorority members had anything to do with Ivins.
"Nothing odd went on," said Graham, an attorney.
Kappa Kappa Gamma executive director Lauren Paitson, reached at the sorority's headquarters in Columbus, Ohio, initially told an AP reporter Monday afternoon she would provide a comment shortly. She did not answer subsequent phone messages or e-mails seeking a response.
Some of the scientist's friends and former co-workers have reacted with skepticism as details about the investigation surfaced. They questioned whether Ivins had the motive to unleash such an attack and whether he could have secretly created the powder form of the deadly toxin without co-workers noticing.
Beginning with cell samples of the anthrax that was mailed in 2001, investigators used advanced to identify unique sections of genetic code that led them to Ivins, according to a government scientist.
Princeton University referred questions about Ivins to the FBI. The university does not formally recognize sororities and fraternities but chapters operate off campus.
Local police in both Princeton Borough and Princeton Township said Ivins' name did not turn up on any incident reports or restraining orders.
Kappa Kappa Gamma also has chapters at nearby colleges in Maryland, Pennsylvania and Washington. One official said investigators were working off the theory that Ivins chose to mail the letters from the Princeton chapter to confuse investigators if he ever were to emerge as a suspect in the case.
Five people died and 17 others sickened by the anthrax plot, which was launched on the heels of the Sept. 11, 2001 terrorist attacks.
The following August, investigators announced they'd found anthrax spores inside the mailbox on Nassau Street, the town's main thoroughfare. FBI agents immediately began canvassing the town, showing residents a photograph of Army scientist Steven J. Hatfill, who at the time was a key "person of interest" in the case.
That theory fell flat and this June, the Justice Department exonerated Hatfill and agreed to a $5.8 million settlement with him.
In the past year, the FBI has turned a close eye on Ivins, whom a therapist said had a history of homicidal and sociopathic behavior. Prosecutors had planned to indict Ivins and seek the death penalty but, knowing investigators were closing in, he killed himself with an overdose of acetaminophen, the key ingredient in Tylenol.
With its top suspect now dead, the Justice Department is considering closing the "Amerithrax" investigations. It has been among the FBI's most publicized unsolved cases and, if it is closed, authorities are expected to unseal court documents that outline much of their case against Ivins.