Lacking hard proof, U.S. federal prosecutors relied on the process of elimination and circumstantial evidence to finger Bruce Ivins as the anthrax killer.
Their case might be compelling, but it is not airtight.
Government investigators didn't place Ivins at the Princeton, New Jersey, mailbox where letters that killed five people were sent. Nor did they present a witness who saw him at work at the Army bioweapons lab at Fort Detrick, Maryland, pouring powder into envelopes. If they found anthrax spores in Ivins' home or cars, they're not saying.
In documents released Wednesday, prosecutors suggested several possible motives, none of them particularly convincing — from concern that the vaccine program Ivins worked in was in trouble to his dislike of Catholic senators who favor abortion rights.
Yet Jeffrey Taylor, the U.S. attorney in Washington, said Wednesday, "We believed we could prove his guilt to a jury beyond a reasonable doubt."
We'll never know. Ivins relieved prosecutors of the challenge of proving their claims when he killed himself last week.
The Justice Department had been down this road before, focusing on an Army scientist as the anthrax culprit. The botched investigation of Steven Hatfill not only led to a $5.8 million settlement with Hatfill, it diverted attention from the real killer.
With Ivins, things were different. A scientific breakthrough gave investigators a powerful tool to trace the anthrax used in the attacks to a single batch that resided in the Fort Detrick lab where Ivins worked. The flask from which the spores were taken was under Ivins' control, Taylor said.
Investigators said in search warrant applications that Ivins misled them by giving them samples from his lab that did not come from the anthrax that was used to make the powder that eventually found its way into the mail.
Lab access records show that he spent an inordinate amount of time in the lab, alone and at night, in the days in September and October 2001 just before two sets of letters were mailed, according to documents released by the government on Wednesday.
The envelopes used in the attacks came from a relatively small defective batch that were sold only in Maryland and Virginia, including at a Frederick, Maryland, post office where Ivins had a box, Taylor said.
Former federal prosecutor E. Lawrence Barcella called the lengthy inquiry into Ivins a classic elimination investigation.
How well it would stand up at trial "depends on how well the elimination went and how narrow the funnel ends up at the end," Barcella said.
Two New Jersey congressman who sat through a private briefing Wednesday came to differing conclusions.
"It is a very compelling case," said Republican Rep. Chris Smith.
Democratic Rep. Rush Holt said he is worried the FBI may have repeated mistakes in looking at Hatfill when they turned their attention to Ivins.
"In both cases, they were looking back in the history of a quirky personality to suggest because of the quirky personality maybe the person would be malicious," Holt said. "That's a leap that you don't usually make in court."
Ultimately, Ivins' personality, his apparent history of emotional problems and increasingly bizarre behavior in the final months of his life would have been invoked by both prosecutors and defense lawyers.
The sworn statements of investigators that supported search warrant applications deal extensively with Ivins' "mental health issues," including odd e-mails and medications prescribed by psychiatrists. They described his apparent obsession with a college sorority, even noting that the Princeton mailbox was less than 100 yards from the sorority's office there.
"They're taking a weird guy and convicting him of mass murder," said Paul Kemp, Ivins' lawyer.
Ivins committed suicide days before prosecutors were scheduled to sit down with Kemp and lay out the government's case. Ivins said he would have demonstrated his client's innocence at trial.
So did he take a drug overdose to spare himself the shame and spotlight of a trial? Or did the pressure of the investigation drive an unstable man to take his own life?
That question will never be answered.
The government, though, is satisfied that after nearly seven years of frustration, it had its man.
Mark Sherman covers legal affairs for The Associated Press.