No-one has yet been charged in relation to the anthrax attacks
US investigators have reportedly found equipment that may have been used in the 2001 anthrax attacks, which left five dead and caused widespread panic in the wake of the 11 September 2001 attacks.
The Washington Post newspaper says that divers from the Federal Bureau of Investigation (FBI) searched a pond in a forested area of Frederick in the state of Maryland following a tip-off in December.
They are said to have found vials wrapped in plastic and a box similar to an airtight chamber with built-in gloves used by scientists to handle dangerous biological or chemical agents.
As well as the five people who died, more than 20 were made ill by letters laced with anthrax that were sent through the mail to various media and political outlets in the country, including the offices of two senators.
The findings have led investigators to formulate a new theory regarding the attacks, whereby the perpetrator created the laced letters in an airtight chamber submerged underwater to avoid exposing himself to the spores or leaving an evidence trail.
Scientists say the pond could be tested for traces of the anthrax spores
The attacker would then have hidden the evidence in the pond.
Some have disputed the theory, saying that the suspect could have engineered the letters on land and simply used the pond to dump evidence.
However, scientists told the paper that investigators could test the pond's sediment for traces of the deadly anthrax spores.
FBI officials have long been baffled by the fact that no traces of anthrax have been found anywhere other the places contaminated by the actual letters.
The discovery has raised fresh hopes of solving the case, which had seemed to be at a standstill after an 18-month long investigation.
The FBI, which has assigned more agents to the case, is now said to be planning to drain more ponds in the area, to search for more evidence.