A third suspect has been identified in connection to the poisoning of a Russian double agent and his daughter in Salisbury, England last year.

Investigative website Bellingcat has named Denis Sergeev, a high-ranking Russian military intelligence officer, as playing a role in the poisoning of Sergei and Yulia Skripal with the Novichok nerve agent A-234 in March 2018.

Sergeev, who goes by the alias Sergey Fedatov, is believed to have worked with two other Russian intelligence officers, Colonel Alexander Mishkin and Colonel Anatoliy Chepiga, to carry out the attempted murders.

Skripal, 66, and his 33-year-old daughter survived the attacks, which caused them to pass out on a public bench while foaming at the mouth. Yulia Skripal had come to Salisbury to visit him the day before the attack, which took effect just after they left Zizzi, an Italian restaurant, in the town.

Skripal worked with the Russian Main Intelligence directorate (also known as GRU) in the 1990s, and passed on information as a double agent for the United Kingdom from 1995 until his arrest in Moscow in 2004. He was jailed in 2006 on charges of high treason, but was later freed in 2010 as a part of a spy trade with the United Kingdom, where he resettled.

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Vladimir Putin was candid with his distaste about the freedom of Skripal and the other spies at the time.

“They will have to hide their whole lives, with no ability to speak with other people, with their loved ones," he reportedly said at the time. “You know, a person who chooses this fate will regret it a thousand times."

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Denis Sergeev's flight records were acquired by Bellingcat, which show that he flew into the United Kingdom on March 2, two days before the Skripals were poisoned. He then reportedly flew back to Moscow on the day of the attack through Rome, instead of on the flight through London that he was previously booked on alongside the other two suspects. His alias of Sergey Fedotov was created in 2010 when he was issued a new passport in Moscow under that name by the same desk which issued passports to the additional two suspects, according to reports.

The other suspects, Mishkin and Chepiga, can be traced to Salisbury on the day of the Skripal attacks, although Sergeev cannot. Both Mishkin and Chepiga deny any involvement in the attack, claiming merely to have been in Salisbury on the day as tourists.

British authorities have yet to officially announce Sergeev as a suspect, but their investigation is ongoing.

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Sergeev was also reportedly present in Bulgaria in 2015 when a local arms dealer was poisoned with a nerve agent similar to the one used on the Skripals.