A Newsnight investigation raised the possibility that there was a secret CIA project to investigate methods of sending anthrax through the mail which went madly out of control.

The shocking assertion is that a key member of the covert operation may have removed, refined and eventually posted weapons-grade anthrax which killed five people.

In the wake of Sept 11th, the anthrax attacks caused panic throughout the States and around the world. But has the FBI found the whole case too hot to handle? Our science editor Susan Watts reported from Washington.

SUSAN WATTS: America's anthrax attack last autumn was second only to that on the Twin Towers in the degree of shock and anxiety it caused...Some even say the anthrax letters triggered sub-clinical hysteria in the American people...yet this, the first major act of biological terrorism the world has seen remains an unsolved crime...

Initially the investigation looked for a possible Al-Qaeda or Iraqi link, then to a domestic terrorist, then inwards to the US bio-defence programme itself. But in the last four or five weeks the investigation seems to have run into the sand...There have been several theories as to why ...

Three weeks ago Dr Barbara Rosenberg - an acknowledged authority on US bio-defence - claimed the FBI is dragging its feet because an arrest would be embarrassing to the US authorities. Tonight on Newsnight, she goes further... suggesting there could have been a secret CIA field project to test the practicalities of sending anthrax through the mail - whose top scientist went badly off the rails...

DR BARBARA ROSENBERG: FEDERATION OF AMERICAN SCIENTISTS: Some very expert field person would have been given this job and it would have been left to him to decide exactly how to carry it out. The result might have been a project gone badly awry if he decided to use it for his own purposes and target the media and the senate for his own motives as not intended by the govt project...but this is a possibility that I think needs to be considered

WATTS: And another leading bio-defence analyst has already sketched out a similar profile for the kind of person likely to be behind the anthrax attacks...

MILTON LEITENBERG: CENTRE FOR INTERNATIONAL & SECURITY STUDIES: UNIVERSITY OF MARYLAND: I would think it was somebody who had this kind of experience, and I think the word that I used for you was 'a cowboy' when we first spoke, that simply means in the United States someone who feels such bravura in his actions, he feels he's a free actor, he can decide what should be done and what shouldn't be done, and what the reason is.

WATTS: In recent weeks, the focus of the investigation has been the US army medical research institute at Fort Detrick near Washington. Fort Detrick is the site at the centre of a web of military centres spread across the US and twilight private companies which work with these military sites hand-in-hand as contractors...

Colonel David Franz was in charge at Fort Detrick for eleven years - he's had hands-on experience with biological agents and has his own ideas about the kind of person the FBI should be looking for.

COLONEL DAVID FRANZ: FORMER DETRICK MEDICAL RESEARCH PROG, 1987-98: It's not someone who just got on the Internet or went to the library and got a book and held the book in one hand and a big wooden spoon in the other and stirred up batches. It's someone who has spent a significant amount of time I believe working with a spore former of some kind and knew how to grow ...and how to purify and how to dry

WATTS: Inside accounts by former staff at Fort Detrick during the nineties reveal a research site in disarray with questionable security measures. We spoke to one former lab technician now working in Belize about unexplained night-time activities in the lab.

DR MARY BETH DOWNS: ST MATTHEW'S UNIVERSITY SCHOOL OF MEDICINE: FORMER FORT DETRICK EMPLOYEE: I came in developed my negatives and here they said anthrax and I looked at this little counter that would have been putting the sequential numbers on the film and there weren't any films missing and yet I knew that Friday I had used it and it hadn't said anthrax.

WATTS: What did that suggest to you had been happening over the weekend?

DOWNS: That someone had been in there working on anthrax....Anyone who did have access to the labs was not monitored in what they did, either in what they did in the lab that is the amount of agent they were growing, or in what they did with that agent, that is if they put it in their pocket and took it home ...

WATTS: Such is the FBI's determination to establish if Fort Detrick is at the heart of this that it has turned to genomic analysis of the powder itself...The Inst for Genomic Research was founded by Craig Venter - the man who sped up the decoding of the Human Genome... their anthrax team has created a DNA "fingerprint" of anthrax taken from the body of the first person to be killed - a Florida-based newspaper man. They're looking for differences between this so-called Florida "strain" and stored samples from a number of US military sites

This is the first time genomic analysis has been used for microbial forensics...Tim Read is one of the world's leading authorities on the genetic make-up of anthrax . He compared the fingerprint of the Florida strain with that of samples originating at Fort Detrick. The results are not yet published - so he's being careful what he says:

DR TIMOTHY READ: THE INSTITUTE OF GENOMIC RESEARCH: They're definitely related to each other ...closely related to each other

WATTS: Could they be so closely related that one could consider them to be one and the same thing?

READ: I'm not commenting on that...

WATTS: But the real answer may lie not just in where the anthrax came from, but who had access to it. Veterans of the 1960s US germ warfare programme were the obvious first thought. Early on in the investigation, there was one name that immediately came to many people, but few dared whisper it aloud. William Capers Patrick the third was part of the original US programme, which officially drew to a close in the 1960s...The New York Times claimed last December he was the author in 1998 of a secret paper study on the possible effects of anthrax sent through the mail, although he now denies that. ...

We went to see Bill Patrick to ask him if he might know the culprit...

Hello Susan Watts BBC

Patrick is an acknowledged showman...known for his startling demonstrations ...some in less than classified company. During the course of our interview he told us several pieces of technical information which one expert said could help anyone intending to create an anthrax weapon.

WILLIAM CAPERS PATRICK III: BIOLOGICAL WARFARE CONSULTANT: I've prepared two harmless simulant powders... beautiful flow properties...

WATTS: It's clear from what Bill Patrick told us that he's been a central figure in the bio-defence community for many years and that he may well have met or come across the person behind the attacks...

PATRICK: Most of my discussions about the biological problem has been in secure conferences and meetings, and involve people with need to know, with security clearance and what have you. I don't talk about 'how to', I don't get into 'how to' with many people, no people other than the fact that those who really have a need to know.

WATTS: Does it nag at you in the back of your mind that possibly you do know him?

PATRICK: Possibly, possibly, I could have talked to these people. But it would have been within the context of their having a need to know.

WATTS: He told me two FBI agents and an official from the attorney general's office interviewed him for 3 and a half hours two weeks ago. He says they told him he had been a suspect, but left him believing he was in the clear.

And just to put on record can I ask you did you perpetrate these attacks..

PATRICK: my goodness I did not ....I did not...I'm an American patriot.

WATTS: Patrick was on the UN team that inspected Iraqi weapons facilities in the mid 1990s, and he WAS surprised the FBI didn't come to him straight after the attacks, simply because of his expertise. He acknowledges it was only logical to consider him a suspect, but for Patrick, the most likely explanation, or perhaps the most comfortable, is that the powder and the motive originated overseas - in some rogue state...

PATRICK: I would hate to think that anyone in our country.. that would do this to our own people, if we ever find whoever does this I hope it comes from overseas, because that way I would.. well I don't want.. I want someone to be caught, I want the perpetrator to be caught, but I would rather think that it came from our enemies outside of our own country as opposed to our own people perpetrating this crime against our own

WATTS: Bill Patrick is no longer seen as a suspect, but the net IS closing around someone at the heart of the US germ warfare programme.

We now know by piecing together information from well-placed sources that there's another individual. He's been interviewed by FBI agents, and remains under widespread suspicion...

But he's no loner. He's likely to have worked on a key government project in the past and to have a network of friends and colleagues he can rely on. The possibility that more than one person is involved may answer some of the perplexing geographical questions about where the attacks originated.

DR RONALD ATLAS: AMERICAN SOCIETY OF MICROBIOLOGISTS: I think that the significance of focussing on a group is that you can have one person with the expertise to produce this weaponised anthrax and someone else to actually deliver it to Trenton. I think that a large part of the investigation early on focused on AN individual. As such we would ask the question, could that individual have gotten to New Jersey. If you begin to think that it could have involved two or more, then the alibi of an individual that I was not near New Jersey may in fact fall apart and you could look at someone else delivering it...

WATTS: The private contractor companies linked to the military and jokingly referred to as "beltway bandits" because they're sprinkled around the Washington beltway ring-road, is where individuals with the right mix of skills might be working. Some of these contractors are now known to have been involved in classified bio-defence projects. One of these secret projects, carried out in the Nevada desert, was part of a series of three In the first few days of September last year - immediately prior to the attacks of the 11th, the New York Times carried a major investigation which at any other time would have been a story of huge significance...It revealed three secret bio-defence projects at a time when the American people believed none was taking place. One - run by a contractor - Battelle - was to create genetically altered anthrax. The question now is - are there more such projects?

MILTON LEITENBERG: UNIVERSITY OF MARYLAND: now we've discovered that the CIA is in this business too, though presumably only through contractors. But we don't know how many contractors. One contractor is now publicly disclosed, Battelle, that did one of those projects. There may be other contractors, so there was this whole story has not been clarified publicly, so that's the rest of your iceberg, in other words we don't know how many contractors, we don't know how many projects.

WATTS: The 1998 paper study on anthrax in the mail was one secret project. Dr Rosenberg is making the astonishing suggestion that there may have been a deadly follow-up by somebody else. Last time she questioned the investigation, she was attacked by the FBI and the White House. But she says she's prepared to speak out again because she's so afraid of what might happen next.

DR BARBARA ROSENBERG: FEDERATION OF AMERICAN SCIENTISTS: This person is.. knows a lot about forensic matters, knows exactly what he can be prosecuted for and what he can get away with and I think he had some personal matters that he might have wanted to settle but I think in addition that he felt that biodefence was being under-emphasised for some time in the past

WATTS: Rosenberg's claims are astonishing but she's an insider with good contacts. She thinks the FBI must act soon.

ROSENBERG: I think the time is rapidly coming when it will be very important to bring him to trial, even if they don't think they have sufficient evidence. This might at least, if not result in a criminal conviction, make it possible to bring civil charges somewhat like what happened to OJ Simpson in the past. So I think it's time to start moving because it's very important from the point of view of deterrence of any possible future terrorist.

WATTS: America's desire to protect its biodefense programme from scrutiny at all costs was part of why it walked away from an international agreement to control biological weapons last summer. Could its near obsessive secrecy have come home to roost? breeding a climate that allowed one of its experts to take a step too far and turn bio-terrorist against his own?

THE FOLLOWING STATEMENT WAS READ OUT AFTER THE BROADCAST : The CIA have told Newsnight they totally reject Dr Rosenberg's theory and say they were unaware of ANY project to assess the impact of anthrax sent through the mail.

* This transcript was produced from the teletext subtitles that are generated live for Newsnight.