Anti-terrorism officials have joined an investigation in southwestern England after two people fell critically ill due to exposure to an “unknown substance” not far from where former Russian spy Sergei Skripal was poisoned in March. Authorities in Wiltshire declared a “major incident” Tuesday and cordoned off several areas after a man and a woman were found unconscious in the town of Amesbury, just eight miles from Salisbury, where Skripal and his daughter, Yulia, were poisoned with a nerve agent in March. London’s Metropolitan Police said Saturday that “given the recent events in Salisbury,” counter-terrorism officers had been called in to join the investigation. Police say they are “keeping an open mind” about the situation but cannot yet say whether a crime has been committed. Samples of the unknown substance have been sent to a laboratory for testing.