U.K. police hunting for source of nerve-agent poisoning after 2 Britons stricken

British police are scouring sections of Salisbury and Amesbury in southwest England for a container feared to be contaminated with traces of the deadly nerve agent Novichok.

More than 100 officers were looking for clues Friday in a race to understand how two local people in Amesbury were exposed to a nerve agentproduced in the Soviet Union during the Cold War.Officers wearingprotective suits also entered a hostel in the nearby cityof Salisbury.

Police believe the couple may have come in contact with a contaminated vial or other item discarded in a public place after a March nerve-agent attack on ex-Russian spy Sergei Skripal and his daughter Yulia in Salisbury. British officials blamed the Skripals'poisoning on Russia. The Kremlin denies any involvement.

The latest victims, Dawn Sturgess, 44, and Charlie Rowley, 45, are still in critical condition. They were hospitalized Saturday after falling ill within hours of each other. At first authorities thought they might have had a bad drug reaction.

Just a few milligrams of the odourless Novichok liquid the weight of a snowflake is enough to kill a person within minutes, experts say, and finding it is the problem.

Police said Friday thatofficers have already spoken to several key witnesses and are poring over more than 1,300 hours of CCTV footage.

Even with the heavy presence of investigators, the probe is expected to take some time.

"Due to the unique challenges involved with this operation, police activity is expected to take weeks and months to complete," a statement from the Metropolitan Police said.

The statement, which includes atimeline tracking the couple's movementsin Salisbury and Amesburyprior to being sickened, notes that so far there's no indication the pair visited any of the sites that were decontaminated after the Skripal poisoning in Salisbury.

"We are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to," the statement said, adding that the investigation into what happened to the Skripals is ongoing.

Difficult to trace

There's no easy way to use technology to locate the container thought to be the source of the Novichok. Instead, there will have to be a laborious physical search of suspected sites, scientists say.

Alastair Hay, professor emeritus of environmental toxicology at the University of Leeds, said there is "no specific method for the detection of Novichoks in the environment" because the use of the nerve agent was not considered likely when monitors were designed.

That means authorities will have to take soil and vegetation samples from sites where it's possible that the nerve agent was present and test the samples in a painstaking process to see if there is any contamination.

A number of sites are being searched in the town of Amesbury, where the couple fell ill, and the nearby city of Salisbury, where the Skripals were poisoned. Forensic searches were due to be carried out at the Amesbury home where Sturgess and Rowley collapsed, and other sites the couple visited before falling ill.

British Home Secretary Sajid Javid told Parliament on Thursday that it's time for Russia to explain "exactly what has gone on."

"It is completely unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns to be dumping grounds for poison," Javid said.

The March attack on the Skripals prompted the biggest Western expulsion ofRussian diplomats since the Cold War as allies sided withBritain's view that Moscow was either responsible or had lostcontrol of the nerve agent.

Moscow hit back by expelling Western diplomats, questioninghow Britain could know that Russia was responsible and offeringrival interpretations, including that it amounted to a plot by British secret services.