Skripal, a former military intelligence officer, was resettled in the English town of Salisbury in 2010, after spending several years in a Russian prison for spying for Britain. But he and his daughter Yulia almost died in March of this year, after being poisoned by a powerful nerve agent that nearly killed them. The attack has been widely blamed on the Russian government, though the Kremlin denies that it had a role in it.

Investigators from Britain and other Western countries have identified the poison used in the attack on the Skripals as novichok. The term (meaning ‘newbie’ in Russian) was given by Western scientists to a series of rarely used nerve agents that were developed the Soviet Union and Russia between 1971 and the early 1990s. It is believed that the poison was smuggled into the United Kingdom hidden inside an imitation perfume bottle, which had been fitted with a custom-made pump used to apply the poison. British authorities have determined that the assailants sprayed the poison on the doorway —including the handle— of the Skripals’ house in Salisbury. They then discarded the perfume bottle, containing the leftover novichok, in a garbage can before leaving the country in a hurry. The bottle was eventually recovered by Salisbury resident Charlie Rowley. His partner, Dawn Sturgess, died of poisoning after she applied some of the contents of the bottle on her wrists. British government scientists have since been examining the contents of the perfume bottle found inside Sturgess’ home.

On Thursday, BBC Television’s Panorama investigative program aired an episode entitled “Salisbury Nerve Agent Attack: The Inside Story”. Among those interviewed was Dean Haydon, a British Deputy Assistant Commissioner who is leading the ongoing investigation into the Salisbury attack. He told Panorama that “a significant amount” of novichuk was left behind by the assailants inside the discarded perfume bottle. The amount of poison in the discarded bottle could have been used to kill “thousands”, he said, adding that the way it was applied to the Skripals’ home was “completely reckless”. The BBC program’s producers also spoke to a British government chemical weapons scientist, identified only as “Tim”, who is credited with having identified the substance used on the Skripals. He told the program that less than 100g of novichuk was used against the Skripals, leaving the vast majority of the nerve agent inside the bottle. Given that novichuk is “one of the deadliest substances known”, which has a “unique ability to poison individuals at very low concentrations”, the scientist said he was shocked by the amount of poison that was smuggled into Britain by the assailants.

The assailants have been identified by British intelligence as Dr. Alexander Yevgenyevich Mishkin (cover name “Alexander Petrov”) and Colonel Anatoliy Chepiga (cover name “Ruslan Boshirov”). Both men are said to be employees of the Russian military intelligence agency known as the Main Directorate of the General Staff of the Armed Forces, commonly referred to as the GRU. Moscow denies that it had any role in the attack on the Skripals.