LONDON (AP) -- Britain's top domestic security official on Thursday described the nerve agent used in the attack on a former Russian spy and his daughter as "very rare," though she refused to say whether investigators know exactly what it is or where it came from.
Home Secretary Amber Rudd told the BBC that enormous resources are being directed at trying to figure out who might be responsible for the poisoning of Sergei Skripal, 66, and his daughter, Yulia, 33. The pair was found unconscious on a bench in the southwestern city of Salisbury on Sunday, triggering a police investigation led by counterterrorism detectives.
"When we have all the evidence of what took place we will, if it is appropriate, attribute it to somebody," Rudd said. "If that is the case, then we will have a plan in place (to respond). We need to be very methodical, take a cool head and be based on the facts, not on rumor."
The Skripal case is reminiscent of the 2006 killing of another former Russian spy who was poisoned in London with radioactive polonium-210. The banned VX nerve agent was used to kill the estranged half-brother of North Korea's leader last year in Malaysia.
Police are focusing their investigation on three locations in Salisbury — Skripal's home, a pub and a restaurant, Rudd said.
Skripal and his daughter are in very serious condition, Rudd said. A police officer who came to their aid is also in a serious situation, though he is not in intensive care.
Police have declined to speculate on who might be behind the attack. The Russian government has denied any involvement in the attack on Skripal, a former Russian agent who had served jail time in his homeland for spying for Britain before being freed in a spy swap.