Ex-Russian spy Sergei Skripal allegedly poisoned: What to know

An ex-Russian spy and his adult daughter remain in critical condition after British authorities said they were poisoned by a nerve agent this month. 

Sergei Skripal, 66, and his 33-year-old daughter Yulia were found unconscious March 4 on a bench in a shopping mall in Salisbury, about 90 miles west of London. 

After the attack, British Prime Minister Theresa May said March 12 that Russia is “highly likely” to be responsible for the poisoning. 

The United States, Germany and France all appear to agree with the United Kingdom that Russia was behind the attack. 

On March 15, President Donald Trump, French President Emmanuel Macron and German Chancellor Angela Merkel, along with May, said in a joint statement that they "abhor" the attack against Skripal.

"It is an assault on U.K. sovereignty and any such use by a State party is a clear violation of the Chemical Weapons Convention and a breach of international law. It threatens the security of us all,” the statement read.

The leaders then called on Russia to "live up to its responsibilities as a member of the UN Security Council to uphold international peace and security,” according to the statement.

May had given Russia until midnight on March 13 to respond to the charges. When Moscow failed to respond, May expelled 23 Russian diplomats from the U.K.

“All who have been identified as declared intelligence officers: they have just one week to leave,” May said. “This will be the single biggest expulsion for over 30 years and it will reflect the fact that this is not the first time the Russian state has acted against our country.”

May said she is also taking diplomatic and economic measures against the country.

Nearly two dozen Russian diplomats expelled by Britain left for Moscow on March 20

In light of the incident, here’s what to know about Skripal:

His background as a spy

Skripal served with Russia’s military intelligence, often known by its Russian-language acronym GRU, and retired in 1999. He then worked at the Foreign Ministry until 2003, and later became involved in business.

Skripal was arrested in 2004 in Moscow and later confessed to having been recruited by British intelligence in 1995. He also said at the time that he provided information about GRU agents in Europe, receiving over $100,000 in return.

At the time of Skripal’s trial, the Russian media quoted the FSB domestic security agency as saying that the damage from his activities could be compared to harm inflicted by Oleg Penkovsky, a GRU colonel who spied for the United States and Britain. Penkovsky was executed in 1963.

In 2006, Skripal was convicted on charges of spying for Britain and sentenced to 13 years. However, he later was pardoned and released from custody in July 2010 as part of a U.S.-Russian spy swap, which followed the exposure of a ring of Russian sleeper agents in the United States.

Skripal’s wife and son have both died in recent years.

Prior to his wife’s death, however, she reportedly told police that she feared for her husband’s life, the New York Daily News reported.

Russia's remarks

British Prime Minister Theresa May has said that that the nerve agent used against the Skripals is called Novichok, a weapon that was developed in the Soviet Union at the end of the Cold War.

Speaking March 18, Russian President Vladimir Putin said that Moscow would cooperate with the U.K. in an investigation of the poisonings, calling them a "tragedy." However, Putin said that if the claims that they were poisoned by the Soviet-designed nerve agent were true, the victims would've died instantly.

"Russia does not have such [nerve] agents," Putin said, according to The Guardian. "We destroyed all our chemical weapons under the supervision of international organizations and we did it first, unlike some of our partners who promised to do it, but unfortunately did not keep their promises.”

Putin added that he thought "any sensible person would understand that it would be rubbish, drivel, nonsense, for Russia to embark on such an escapade on the eve of a presidential election."

Putin's remarks came after Russia earlier retaliated against the U.K.: Moscow announced March 17 that it also would expel 23 British diplomats, among other diplomatic measures.

Fox News’ Kathleen Joyce, Katherine Lam, Travis Fedschun, Lucia I. Suarez Sang, Madeline Farber, Zoe Szathmary, Nicole Darrah and The Associated Press contributed to this report.