by Cather­ine Her­ridge and Ian McCaleb
FOXNews.com

WASHINGTON —
The FBI has nar­rowed its focus to “about four” sus­pects in the 6 1/2‑year inves­ti­ga­tion of the dead­ly anthrax attacks of 2001, and at least three of those sus­pects are linked to the Army’s bioweapons research facil­i­ty at Fort Det­rick in Mary­land, FOX News has learned.

Among the pool of sus­pects are three sci­en­tists — a for­mer deputy com­man­der, a lead­ing anthrax sci­en­tist and a micro­bi­ol­o­gist — linked to the research facil­i­ty, known as USAMRIID.

The FBI has col­lect­ed writ­ing sam­ples from the three sci­en­tists in an effort to match them to the writer of anthrax-laced let­ters that were mailed to two U.S. sen­a­tors and at least two news out­lets in the fall of 2001, a law enforce­ment source con­firmed.

The anthrax attacks began short­ly after the Sept. 11, 2001, ter­ror attacks, fur­ther alarm­ing a nation already reel­ing from the deaths of 3,000 Amer­i­cans. Five peo­ple were killed and more than a dozen oth­ers were infect­ed by the dead­ly spores in the fall of 2001.

A lead­ing the­o­ry is that the anthrax was stolen from Fort Det­rick and then sealed inside the let­ters. A law enforce­ment source said the FBI is essen­tial­ly engaged in a process of elim­i­na­tion.

Much of the ear­ly pub­lic focus fell on a Fort Det­rick sci­en­tist named Steven Hat­fill, who is suing fed­er­al author­i­ties for iden­ti­fy­ing him as a per­son of inter­est. Now the FBI is focus­ing on oth­er sci­en­tists at the facil­i­ty.

“Fort Det­rick is run by the Unit­ed States Army. It’s the most secure bio­log­i­cal war­fare research cen­ter in the Unit­ed States,” a bioter­ror­ism expert told FOX News.

Asked to com­ment on the like­li­hood that the anthrax orig­i­nat­ed at the facil­i­ty, the expert said:

“It’s not supris­ing, except that it would under­score that there was seri­ous secu­ri­ty defi­cien­cies that exist­ed at one time at Fort Det­rick — the abil­i­ty of researchers to smug­gle out some type of very sophis­ti­cat­ed anthrax weapon and in some quan­ti­ty. And, nev­er­the­less, it was pos­si­ble.”

In Decem­ber 2001, an Army com­man­der tried to dis­pel the pos­si­bil­i­ty of a con­nec­tion to Fort Det­rick by tak­ing the media on a rare tour of the base. The com­man­der said the Army used only liq­uid anthrax, not pow­der, for its exper­i­ments.

“I would say that it does not come from our stocks, because we do not use that dry mate­r­i­al,” Maj. Gen. John Park­er said. The let­ters that were mailed to the media and Sens. Tom Daschle and Patrick Leahy all con­tained pow­dered anthrax.

But in an e‑mail obtained by FOX News, sci­en­tists at Fort Det­rick open­ly dis­cussed how the anthrax pow­der they were asked to ana­lyze after the attacks was near­ly iden­ti­cal to that made by one of their col­leagues.

“Then he said he had to look at a lot of sam­ples that the FBI had pre­pared ... to dupli­cate the let­ter mate­r­i­al,” the e‑mail reads. “Then the bomb­shell. He said that the best dupli­ca­tion of the mate­r­i­al was the stuff made by [name redact­ed]. He said that it was almost exact­ly the same … his knees got shaky and he sput­tered, ‘But I told the Gen­er­al we did­n’t make spore pow­der!’ ”

Asked for com­ment, an Army spokes­woman referred all calls to the FBI. The FBI would not com­ment about the pool of sus­pects, but a spokes­woman said the inves­ti­ga­tion clear­ly remains a pri­or­i­ty.