British police were scrambling on Monday to solve the mystery surrounding the death of a woman following her exposure to the Novichok nerve agent last week. Prime Minister Theresa May said she was "appalled and shocked" by the death of Dawn Sturgess, a 44-year-old mother of three who had been living in a homeless hostel in the city of Salisbury in southwest England. The death on Sunday occurred four months after the same toxin was used against a former Russian spy in an attack that Britain blamed on Moscow. Sturgess and Charlie Rowley, 45, fell ill last weekend in the town of Amesbury, near Salisbury, the city where former double agent Sergei Skripal and his daughter Yulia were attacked with the Novichok nerve agent in March and have since recovered. Local MP John Glen said the local community was "anxious" after police opened a murder inquiry, although health officials have said the danger to the general public is low. Glen told BBC radio the two may have handled a contaminated object because of their "habit of looking into bins" and police were trying to work out "how they came into contact with this nerve agent and when". Police said they would be led by the evidence but confirmed a link between the Amesbury case and the Salisbury attack was a main line of inquiry. The attack on the Skripals prompted the biggest Western expulsion of Russian diplomats since the Cold War as allies sided with Britain’s view that Moscow was either responsible or had lost control of the nerve agent. Moscow hit back by expelling Western diplomats. Russia has denied any involvement in the Skripal case and suggested the British security services had carried out the attack to stoke anti-Moscow hysteria. Interior minister Sajid Javid last week demanded answers from Moscow, saying he would not accept Britain becoming a "dumping ground for poison". Russia hit back, denouncing Britain for playing "dirty political games". Police said the British couple were believed to have become exposed to Novichok by handling a "contaminated item", with speculation that it could have been the container used to administer the nerve agent to the Skripals. However, police and public health officials insist the risk to the wider public remains low. A police officer was tested for possible exposure to the deadly nerve agent over the weekend but was given the all-clear. Christine Blanshard, medical director at Salisbury District Hospital, where Sturgess and Rowley were being treated and where the Skripals were hospitalized, told the Daily Telegraph that staff had "worked tirelessly to save Dawn". "Our staff are talented, dedicated and professional and I know today they will be hurting today," she said. The prime minister said: "Police and security officials are working urgently to establish the facts of this incident, which is now being investigated as a murder." Assistant Commissioner Neil Basu, the head of Britains counter-terror police, said Sturgesss death "has only served to strengthen our resolve to identify and bring to justice the person or persons responsible for what I can only describe as an outrageous, reckless and barbaric act". He added that the other victim "remains critically ill in hospital and our thoughts are with him and his family as well". Alastair Hay, a professor of environmental toxicology at Leeds University, said the hospital probably now had more experience than anywhere else in the world with Novichok cases, but there were limits to what doctors could do. “Because the nerve agents compromise nerve and muscle function, their effects are widespread and where deaths occur these are usually due to either respiratory or circulatory failure, or both,” he said. Residents of the homeless hostel in Salisbury where Sturgess lived, which was evacuated after the couple fell ill, expressed their devastation at the news of her death. "It could easily have happened to anyone, to me or my partner," 27-year-old Ben Jordan told AFP late Sunday. "We are really, really sad. I am praying for Charlie." Around 100 counter-terrorism officers are helping in the investigation, which police said Friday could take "weeks and months". So far, there is no evidence that the couple visited any of the sites involved in the Skripal case.