LONDON, U.K. - The poisoning of a former Russian double agent, 66-year-old Sergei Skripal with a nerve agent in the U.K. has threatened ties between the two nations as Britain continued investigation into the poisoning and Russia mocked the paranoia over the entire incident.

On Friday, authorities in the U.K. said that they were re-examining their theories about where and how the former spy could have been poisoned.

What has made matters worse for investigators is the fact that almost two dozen first responders and medical staff came in contact with Skripal and his daughter in the minutes after they fell violently ill - but only one of them became sick from the deadly toxin.

Earlier this week, British authorities revealed that Skripal was found slumped over and unresponsive next to his 33-year-old daughter, Yulia, on a bench outside a shopping mall in Salisbury, England. 

Jaime Paine, who found the duo, alerted the police and told the local media, "When she was on the floor, her eyes were just completely white. They were wide open but just white and (she was) frothing at the mouth. Then the man went stiff. His arms stopped moving, but he's still looking dead straight."

Even 48 hours post their discovery, the police were trying to figure out what sickened the former Russian spy.

Police described it as an illness triggered by exposure to an unknown substance.

Soon, the counter-terrorism police took over the investigation of the illness and Mark Rowley, head of U.K. counter-terrorism police said in a statement, "The critical thing is to get to the bottom of what's caused this illness as quickly as possible. As you'd expect, the special resources that work within the counter-terrorism network that I coordinate across the country and other partners are working with Wiltshire police."

British troops, trained in chemical warfare began assisting with the probe after officials in the country declared that the duo had been poisoned by a rare nerve agent.

The usually sleepy English city of Salisbury became an active part of the investigation as armed soldiers and forensic experts in bright yellow hazmat suits spread across the city and especially at some key points where the ex-spy and his daughter were sighted.

On Friday, U.K. authorities said they were re-examining their theories about where and how Skripal and his daughter were poisoned with the nerve agent.

Over the last week, police have been painstakingly reconstructing the pair's movements that afternoon by canvassing witnesses and examining CCTV footage.

Forensic experts in hazmat suits took over the Italian restaurant where the duo ate lunch and the local pub where they stopped for a pint.

Police have also turned their focus on Skripal's house which is nearby and have cordoning off the property.

Forensic tents have been erected in the former spy's garden and now investigators are trying to establish if the nerve agent was inadvertently delivered at home.

Det.-Sgt. Nick Bailey sickness from the deadly toxin has proved to be a major challenge for investigators too.

According to officials, about two dozen first responders and medical staff came in contact with Skripal and his daughter after they fell violently ill but only Det.-Sgt. Nick Bailey became sick.

Bailey was the first policeman to visit Skripal's home and is currently in a serious condition, but is able to speak.

Investigators are also believed to be examining whether Yulia, who was visiting from Moscow, unknowingly brought the nerve agent along in food or drink, or maybe in a gift.

Skripal and his daughter are still critically ill and are being treated in intensive care.

Who is Sergei Skripal?

Skripal, who is a former Russian military intelligence officer, was convicted in 2006 of "high treason and spying" for Britain and had been sentenced to 13 years in jail by a Russian court.

He was discovered to have passed sensitive information to MI6, the British intelligence service, in exchange for cash since the early 1990s.

In July 2010, he was pardoned by then-Russian president Dmitry Medvedev and released by Moscow.

He was flown to Vienna, Austria along with three other accused spies and was part of a Cold War-style spy swap - in return for ten Russian agents, deep-cover "sleeper agents" who were operating for Russia in the U.S.

The infamous Anna Chapman, Russian President Vladimir Putin's glamour spy, was believed to be part of this exchange.

The 66-year-old former agent later settled in the sleepy cathedral town of Salisbury, southwest of London and seems to have led a quiet life there, living at a modest suburban house.

British authorities have voiced their suspicions of Russian involvement in the poisoning but have not officially accused the Kremlin of trying to assassinate a U.K. resident on British soil.

Earlier in the week however, Britain warned Russian that it would respond strictly if the Kremlin was behind the poisoning of the former double agent.

The U.K. Foreign Secretary Boris Johnson told the British parliament on Tuesday, "We don't know exactly what has taken place in Salisbury, but if it's as bad as it looks, it is another crime in the litany of crimes that we can lay at Russia's door. It is clear that Russia, I'm afraid, is now in many respects a malign and disruptive force, and the U.K. is in the lead across the world in trying to counteract that activity."

Johnson said that "if Moscow was shown to be behind Skripal's illness, it would be difficult to see how U.K. representation could go to the World Cup in Russia in a normal way."

However, the Russian Foreign Ministry spokeswoman Maria Zakharova immediately responded and called Johnson's comments "wild."

The Russian government also released an official statement claiming that it had no information about the incident.

Kremlin spokesman Dmitri Peskov, said accusations of Kremlin involvement "weren't long in coming."

He added, "You know how he ended up in the West, what actions and decisions led him there."

But as the week drew to a close, Russians were seen to be openly mocking efforts by the U.K. to link Kremlin to the case.

Russian media painted it as some sort of "Western conspiracy."

A Russian state TV anchor took evident delight in Skripal's illness on Friday.

Kirill Kleimenov, who hosts Channel One's main evening news broadcast reportedly said on his show, "The profession of a traitor is one of the most dangerous in the world. It's very rare that those who had chosen it have lived in peace until a ripe old age."

He then added a warning to people "who hate their country," and said, "Don't choose Britain as a place to live. Something is wrong there. Maybe it's the climate, but in recent years, there have been too many strange incidents with grave outcomes there."