A spokesman for the Justice Department, Dean Boyd, said Thursday that uncertainty about the origin of the anthrax used in the mailings had prevented investigators from narrowing their search earlier. Boyd said that years of "analysis and review" led to Ivins. Officials were not prepared to respond to detailed questions posed for this article, he said.
Investigating the mailings presented a steep challenge for the FBI, which was not equipped to analyze the recovered anthrax in a way that might yield a DNA "signature" identifying the source of the material. Indeed, in fall 2001, the FBI immediately turned to Ivins and others at the U.S. Army Medical Research Institute of Infectious Diseases, within Ft. Detrick, for scientific assistance.
When they unveiled their evidence against Ivins last week, federal law enforcement officials did not mention the bleaching that Ivins had performed in the aftermath of the mailings, nor did they discuss any of the other conduct described by the Army in its May 2002 report.
The federal officials who spoke publicly last week also did not specify when the FBI first examined the access-card records at Ft. Detrick that documented Ivins' string of late-night visits to the hot suite.
Another crucial aspect of the investigation, the genetic analysis of the powder, was first performed in 2002 and suggested, but did not prove, that Ft. Detrick was the most likely source. Federal officials say proof came with refined testing capabilities available more recently.
Relying on the new technology and conventional police work, officials believe that they have conclusively tied the material gathered from the mailings to a single flask under Ivins' control -- the flask with the RMR-1029 spores that agents had first sought from him in early 2002.
As for Hatfill, the former Ft. Detrick researcher with no record of access at any time to anthrax, FBI and Justice Department officials have declined to say why the investigation stayed focused on him for so long.
Several officials told reporters last week that they did not turn to Ivins as a suspect until last year because they had lacked the breakthrough scientific data and other recently gathered evidence tying him to the mailings.
"In an investigation of this scope and complexity, the task is to follow the evidence where it leads," Jeffrey A. Taylor, U.S. attorney for Washington, D.C., told reporters last week.
