[3] In December 2004, he was arrested by Russia's Federal Security Service (FSB) and later tried, convicted of high treason, and sentenced to 13 years in prison.
[4][5] On 4 March 2018, he and his daughter Yulia, a Russian citizen who was visiting him from Moscow, were poisoned with a Russian-developed Novichok nerve agent,[6][7] and were admitted to Salisbury District Hospital in a critical condition.
[11] In 1972, Skripal completed the Zhdanov military engineering school in Kaliningrad, located in the village of Borisovo (formerly Kraußen (Königsberg))[13] with the qualification of a sapper-paratrooper.
[14] He then studied at the Moscow Military Engineering Academy and subsequently served in the Soviet Airborne Troops where he was deployed to Afghanistan during the Soviet–Afghan War under the command of Boris Gromov.
[24] Amid controversial circumstances, he was convicted under "Article 275" of the Russian Criminal Code (high treason in the form of espionage) by the Moscow Regional Military Court in a trial conducted behind closed doors.
[23] The prosecution, which was represented by Chief Military Prosecutor Sergei Fridinsky, argued for a 15-year sentence – instead of the 20-year maximum under Article 275 – in recognition of mitigating circumstances such as his cooperation with investigators.
[26] Skripal's lawyers appealed the sentence,[citation needed] which was upheld by the Military Collegium of the Supreme Court on 30 November 2006.
[33] According to British security officials, Skripal continued to provide information to the UK and other Western intelligence agencies for a period after 2010.
While living in Britain, he had travelled to other countries, meeting with intelligence officials of the Czech Republic, Estonia, and Colombia, most likely discussing Russian spying techniques.
He provided information to the Estonian secret service in Tallinn, which enabled them to identify three active Russian undercover operatives.
[48] On 4 March 2018, Skripal and his 33-year-old daughter Yulia, who was visiting from Moscow, were found "slipping in and out of consciousness on a public bench"[49] near a shopping centre in Salisbury by a doctor and nurse who were passing by.
[55][56] Two police officers were treated for possible minor symptoms, said to be itchy eyes and wheezing, while a third, Detective Sergeant Nick Bailey, who had been sent to Sergei Skripal's house, was in a serious condition.
Assistant Commissioner Mark Rowley, head of Counter Terrorism Policing, appealed for witnesses to the incident following a COBR meeting chaired by Home Secretary Amber Rudd.
[67] On 31 March 2018 the BBC reported that the UK was considering the Russian Embassy's request, 'in line with its obligations under international and domestic law.
[69][70] On 30 June 2018, two British Nationals were hospitalized by chemical poisoning in Amesbury, 8 miles (13 km) from Salisbury where Skripal had been attacked.
[71] On 16 February 2019 The Sunday Times reported, without identifying sources, that Sergei Skripal "has suffered a deterioration in his health and is being treated by doctors".