In this Friday, July 6, 2018 file photo, an elderly man walks by as British police officers guard metal fencing surrounding tents set up by search teams at the end of Rollestone Street, outside the location of the John Baker House for homeless people in Salisbury, England. British detectives investigating the poisoning of two people by the nerve agent Novichok in southern England said Friday, July 13, 2018 that scientists have found the source of the deadly substance. (AP Photo/Matt Dunham)
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