In towns and villages across Kosovo, teams of war crimes investigators are working against the clock.

A month after they first entered the war-torn province under the auspices of the International Criminal Tribunal for the former Yugoslavia, the investigators, currently numbering at least 100, are trying to assemble evidence that will help bring Yugoslavia's President Slobodan Milosevic to trial.

The teams, drawn from at least 12 countries, include experts in forensic science, pathology, ballistics and detectives experienced in finding the smallest clue at the scene of the crime.

Jim Landale, spokesman for the ICTY, has recently returned from the field and said that the teams were following a three-step plan to gather evidence.

"When the refugees started flowing across the borders, we got investigators to them to record as much testimony as possible.

"All this information is being entered into a database so that it can be analysed and cross-referenced so that we can build up a significant picture of what happened."

As the estimate of the number of suspected war crimes sites reached 300, the ICTY recognised that the scale of the task was becoming enormous and it would have to concentrate on key massacre sites.

Such is the weight of the work, some sites will never be investigated before evidence is lost forever.

The ICTY, working under the direction of outgoing chief prosecutor Louise Arbour, is focussing on seven priority sites included in the Milosevic indictment. A second list of sites has not been released to the public.

British forensic teams, among the first to enter the province, were sent immediately to Velika Krusa, the scene of some of the most appalling killings, while advanced K-For units headed for other areas to seal off sites for investigators.

Slow progress: Piecing together evidence

"When we went in, there was a real sense of urgency," said Mr Landale.

"We wanted to focus on the surface remains which will perish or be at risk of being polluted of damaged.

"We have even heard of dogs taking away body parts and reburials also damage evidence.

"We can get to the graves later because they hold the information much longer."

The BBC's Michael Voss in Kosovo reports on the work of the war crimes investigators

Where the investigators have found bodies, or the remains of bodies, these are being pieced together to establish identity and link the dead to any evidence provided by refugees.

Weapons experts are attempting to link bullets and shell casings to the Yugoslav military.

The German team is using three-dimensional computer software to create a digital model of war crimes sites, invaluable in mapping the progress of the war against civilians.

But perhaps the most critical investigations are taking place in archives, and in the wider intelligence community.

"Our third task is to prove the chain of command," said Mr Landale.

"We have to do this if we are going to prosecute Slobodan Milosevic.

"The investigators are co-operating with various states because gathering intelligence information is a very important aspect of this.

"This is not just information gathered in the field but also intercepts of communications, aerial photography and such like.

"This side of the investigation is, of course, very sensitive. The states that are willing to co-operate must have confidence in us."

Timescale

Since its establishment in 1993, the ICTY has been criticised for the speed at which it has worked.

Physical evidence: Carefully documented

As of May, the tribunal had publicly indicted 84 people.

Six of the indictees have already died, charges against another 18 were dropped.

Two indictees have been tried and sentenced - one has served his sentence and one is currently serving his sentence. A third was acquitted.

A further 25 are currently in custody. Among those still at large are the former Bosnian Serb leader Radovan Karadzic and his military commander Ratko Mladic.

In its defence, the ICTY says that its budget is tight and it has no police force of its own to arrest suspects. It relies solely on the work of S-For in Bosnia and now K-For in Kosovo to make arrests, organisations which are ultimately under political control elsewhere.

Chain of command: Investigators search for documents

Mr Landale said: "This process is evidence driven. The chief prosecutor has to feel that she has got a prima facie case otherwise the judge will throw it out.

"As for suspects, we would like to see them in The Hague as quickly as possible.

"But we have not got our own police force.

"In the case of [suspects in] Serbia, that is very difficult but we want others in relevant positions to bring people to custody."

The practicalities of actually bringing the Yugoslav leadership to book for crimes in Kosovo remains highly problematic.

But as far as the investigators are concerned, that is a matter for others to deal with, said Mr Landale.

"Day in and day out they are working in very difficult circumstances.