Detectives investigating the attempted murders of Russian double agent Sergei Skripal and his daughter Yulia Skripal have said they believe the pair were poisoned with a nerve agent at the front door of his Salisbury home. 
 
 Specialists investigating the poisoning of the the Skripals have found the highest concentration of the nerve agent on the front door at the address, police said. 
 
 Counter-terrorism detectives will continue to focus their inquiries on the home address for the coming weeks, and possibly months, after the father and daughter were found unconscious on a park bench in Salisbury earlier this month. 
 
 Sergei and Yulia Skripal have slim chance of survival, says niece Read more 
 
 Local police have retaken control of The Maltings shopping centre, where the Skripals were first discovered, and London Road cemetery from counter-terrorism detectives, where officers focused their investigation into the nerve agent attack in previous weeks. 
 
 More than 130 people could have been exposed to the chemical weapon in the aftermath of the poisoning in Salisbury, which the UK government believes was committed by the Russian state. 
 
 In response to the poisoning, more than 150 Russian officials have been expelled from more than 25 countries, and the UK government is considering further measures to punish Russia, including a ban on the City of London from selling Russian sovereign debt. 
 
 Public health experts are still working to establish whether the nerve agent attack presents a long term risks to Salisbury’s residents, which will receive a £1m support package from central government to help recover. 
 
 Deputy assistant commissioner Dean Haydon, the senior national coordinator for counterterrorism policing, said: “At this point in our investigation, we believe the Skripals first came into contact with the nerve agent from their front door. 
 
 “We are therefore focusing much of our efforts in and around their address. Those living in the Skripals’ neighbourhood can expect to see officers carrying out searches as part of this but I want to reassure them that the risk remains low and our searches are precautionary. 
 
 “I’d also like to thank the local community for their continued support and understanding. The unique circumstances of this investigation means that officers are likely be in the area for several weeks and months.” 
 
 About 250 counter-terrorism detectives continue to work around the clock on the investigation, supported by a full range of experts and partners. Officers continue to trawl through more than 5,000 hours of CCTV and examine more than 1,350 exhibits that have been seized. Approximately 500 witnesses have been identified and hundreds of statements taken. 
 
 Traces of the nerve agent have been found at some of the other scenes detectives have been working at over the past few weeks, but at lower concentrations than that found at the home address. ||||| A Russian hit squad poisoned Sergei Skripal and his daughter by smearing nerve agent on his front door, police disclosed last night. 
 
 Counter-terrorism police revealed for the first time that they believed Colonel Skripal and his daughter Yulia "first came into contact" with the Novichok nerve agent at their home. 
 
 Scotland Yard added that the "highest concentration of the nerve agent" had been discovered on the front door of Col Skripal's home in a cul-de-sac close to Salisbury city centre. 
 
 Detective Sergeant Nick Bailey, who was also hospitalised, is thought to have become ill after going to the house and was one of the first on the scene. 
 
 The disclosure will intensify the manhunt for the would-be assassins who had targeted Col Skripal, 66, and his 33-year-old daughter. It will also heap further pressure on the Kremlin, which is accused of being behind the attack, for putting at risk anybody who had gone to the Skripals' home. ||||| (CNN) Detectives with London's Metropolitan Police said Wednesday they believe former Russian double agent Sergei Skripal and his daughter first came into contact with a nerve agent at Sergei Skripal's home, and police have identified the highest concentration of the nerve agent to date as being on the home's front door. 
 
 The pair were poisoned March 4 after being exposed to what British police believe was a military-grade nerve agent. They are hospitalized in critical condition. 
 
 Skripal and his daughter, Yulia, were found slumped on a bench in an outdoor shopping complex in Salisbury, England. They had no visible injuries, according to police. 
 
 They were near a number of restaurants, one of which was closed as part of the initial investigation. 
 
 Detectives now plan to focus their investigation around Sergei Skripal's Salisbury home for the coming weeks and possibly months, the Met Police said. Yulia Skripal was visiting her father. 
 
 Police also plan to search the surrounding area. 
 
 Yulia Skripal 
 
 "Those living in the Skripals' neighborhood can expect to see officers carrying out searches as part of this, but I want to reassure them that the risk remains low and our searches are precautionary," Deputy Assistant Commissioner Dean Haydon said in a statement. 
 
 Around 250 counterterrorism detectives are working around the clock on the investigation, the Met Police said, adding it is one of the largest and most complex investigations undertaken by British counterterrorism police. 
 
 Officers are examining more than 5,000 hours of closed-circuit television and more than 1,350 seized items, police said. They have identified around 500 witnesses and taken hundreds of statements. 
 
 Detectives have found traces of the nerve agent at other scenes in the past few weeks but at lower concentrations than at the home address, the Met Police said. 
 
 Surveillance footage shows Sergei Skripal shopping at a convenience store days before he was poisoned. 
 
 Diplomatic fallout 
 
 The UK has expelled 23 Russian diplomats over the poisoning of the Skripals, which it blames on Moscow. Russia denies it was involved and has suggested the UK could be behind it. 
 
 In a show of support for Britain, more than 20 other countries have kicked out Russian diplomats . Those countries include the United States, Canada, Australia and 18 European Union states. 
 
 In a speech Wednesday evening, British Foreign Minister Boris Johnson thanked the countries "from the bottom of my heart" for standing with Britain, saying they did it despite the risk of retaliation. 
 
 "I believe that these expulsions represent a moment when a feeling has suddenly crystallized, when years of vexation and provocation have worn collective patience to (the) breaking point, and when across the world -- across three continents -- there are countries who are willing to say enough is enough," Johnson said at an annual gathering of the diplomatic corps in London. 
 
 Russian Foreign Minister Sergey Lavrov said the United States pressured and blackmailed other countries to expel Russian diplomats. 
 
 British Prime Minister Theresa May speaks Monday in Parliament. 
 
 Moscow has already responded by expelling 23 British diplomats and shuttering British cultural institutions in Russia. Tuesday, Lavrov warned of further retaliation , saying, "Rest assured, we will respond," according to state media. 
 
 Russia's ambassador to Australia called the expulsions "unfair." 
 
 "It's rather like the beginning of 'Crime and Punishment,'" Johnson said. "We're all confident of the culprit, and the only question is whether he will first confess or be caught." 
 
 The Skripals 'may never fully recover' 
 
 According to the UK, the Skripals were exposed to a Soviet-era nerve agent known as Novichok, a colorless, odorless and tasteless liquid described as one of the world's most sophisticated and deadly chemical weapons. 
 
 While British officials have said they believe the public health risk is low, Prime Minister Theresa May has also said more than 130 people in Salisbury could have been exposed to the nerve agent. 
 
 May said Monday that doctors have indicated the Skripals may never fully recover. 
 
 "This shows the utterly barbaric nature of this act and the dangers that hundreds of innocent citizens in Salisbury could have faced," May said. 
 
 Johnson said Wednesday that the Kremlin underestimated the global response to the poisoning. 
 
 "If they thought that the world had become so hardened and so cynical as not to care about the use of chemical weapons in a place like Salisbury," he said, "if they believed that no one would give a fig about the suffering of Sergei and Yulia Skripal, or that we would be indifferent to the reckless and contemptuous disregard for public safety ... then this is their answer."
– The military-grade nerve agent that left former Russian double agent Sergei Skripal and his daughter near death appears to have been left on his front door in Salisbury, England, police say. Investigators say the Skripals first came into contact with the nerve agent at Skripal's home, and the highest concentration of it was found on the door, the Guardian reports. Skripal and his daughter, Yulia, were found unconscious on a bench at an outdoor shopping complex on March 4. Detective Sergeant Nick Bailey, who was hospitalized for more than two weeks after the incident, is believed to have become sick after visiting the Skripal house, where he was one of the first on the scene, reports the Telegraph. Police say residents of Skripal's neighborhood can expect more searches in the area, but "the risk remains low." Britain blames Russia for the attack. It has expelled 23 Russian diplomats and numerous other countries, including the US, have followed suit. In a speech late Wednesday, British Foreign Secretary Boris Johnson thanked Britain's allies "from the bottom of his heart," CNN reports. "I believe that these expulsions represent a moment when a feeling has suddenly crystallized, when years of vexation and provocation have worn collective patience to (the) breaking point, and when across the world—across three continents—there are countries who are willing to say enough is enough," he said. (A relative says there is almost no chance the Skripals will survive.)