Complex and dangerous, nerve agents are rarely used for assassinations

Thousands of people have been fatally gassed with nerve agents on battlefields since World War Two, most recently in Iraq and Syria, but they are not a weapon of choice for urban assassinations.Sergei Skripal, a 66-year-old former Russian double agent, and his 33-year-old daughter Yulia were poisoned with a rare toxin on Sunday at a shopping mall in Salisbury, southern England, and remain critically ill in hospital, police said.