
This is the extraordinary 30-hour assassination mission to Salisbury that Britain believes was carried out by members of Putin's feared military intelligence service specially trained to hunt down and punish traitors.

A team of up to four spies including a woman are claimed to have been sent to murder double agent Sergei Skripal and his daughter Yulia - two agents to carry and administer the Novichok and two more as back up in case their comrades fell ill or failed.

Numerous security sources say the hit squad was probably made up of existing or former GRU agents not known to MI6 who may even have followed Yulia from Moscow to London on March 3.

Miss Skripal and her double agent father fell ill in Salisbury on March 4 and the assassins dumped the poison hidden in a perfume bottle in the Wiltshire city's Queen Elizabeth Gardens where ill-fated couple Dawn Sturgess and Charlie Rowley found it four months later.

The team fled to Heathrow where they are believed to have flown to Moscow on an Aeroflot jet on March 5 - 30 hours after they arrived - shunning the usual circuitous spy route home via an airport in the Mediterranean, Scandinavia, Switzerland or Turkey.

The same day a British listening station in Cyprus is understood to have intercepted a coded message to Moscow that included the phrase: ‘The package has been delivered’ and said the team has 'made a successful egress'.

An Aeroflot flight that landed in London on March 30 was boarded by UK's border force for a 'routine' search - but MailOnline has studied its flight data and can reveal this is the same plane that may have carried the assassins home on March 5.

The inspection caused fury in Russia, whose diplomatic officials called it a 'blatant provocation', and its embassy in London was reportedly sufficiently concerned about the aircraft being examined to rush diplomatic staff to Heathrow.

Yesterday CNN reported that using facial recognition technology police and the secret services who pored over 4,000 hours of CCTV footage in Salisbury and UK airports identified the spies now wanted for the March 4 attack - and Dawn Sturgess' murder.

Spooks also know the 'fresh identities' used to get back to Russia after cross-referencing their passport aliases with the commercial flight's manifest.

This map shows how the assassins are believed to have escaped Britain. They poisoned the Skripals and are then thought to have dumped Novichok in a Salisbury park before fleeing to Heathrow to board a commercial flight to Russia as a coded message was then intercepted by an RAF base in Cyprus. This same plane was searched three weeks later when it returned to London, causing a further diplomatic row with Russia

Sergei Skripal gave secrets to the British and would settle in Salisbury near Porton Down before the assassination attempt on March 4

This is the Aeroflot jet searched by British authorities several weeks after the poisoning, believing it was the one the assassins flew on

Security sources speaking shortly after the poisoning said investigators were examining the flight list for Mr Skripal's daughter's flight to the UK and believed the assassins fled back to Moscow within hours of delivering the lethal agent.

Sergei Skripal was held for two years before being convicted of passing secrets to the British (pictured during his arrest in 2004) but would later be freed during a spy swap in 2010

It was also said at the time that spy agencies had 'red-flagged' an individual who arrived on a flight from Moscow the day before the Skripals were poisoned.

GRU agents are believed to have been chosen to carry out the mission.

Sergei Skripal was a colonel in Russia's military intelligence until he defected to Britain.

Former members brave enough to speak out say that once a member of the GRU, it is exceptionally difficult to leave.

And those who do so to join foreign agencies are punished savagely.

Viktor Suvorov, a GRU officer who defected to Britain in 1978, said new recruits were shown a video of a traitor from the agency being burned alive in a furnace as a warning.

They also believe that traitors must face the "ultimate punishment" - death - and Vladimir Putin has previously said that it 'always ends in a bad way' for those who betray Russia.

Mr Skripal retired from military intelligence, often known by its Russian-language acronym GRU. He went on to work at the Foreign Ministry until 2003.

He was arrested in 2004 in Moscow and admitted he was recruited by British intelligence in 1995 and had provided information about GRU agents in Europe, for which he was paid more than $100,000.

Mr Skripal was one of four agents pardoned and released by Moscow in what was said at the time to be the biggest spy swap since the Cold War.

He was flown to the UK with another of the men freed by Russia in the exchange - analyst Igor Sutyagin, who was serving a 14-year sentence for spying for the US.

The spy swap took place on July 9, 2010 on the tarmac at Vienna's airport and a Boeing 767-200 carrying the four agents was understood to have later touched down at RAF Brize Norton in Oxfordshire.

The returning Russian spies were greeted as heroes in Moscow. Mr Putin, himself a former KGB officer who served in what was then East Germany, sang patriotic songs with them.

But Mr Putin predicted a grim future for the man who had betrayed the Russian spies in the US, saying that he knew both his identity and location.

He said that a 'Mercader has already been sent after him,' referring to Ramon Mercader, the assassin who was sent to kill Leon Trotsky in 1940 in Mexico.

Mr Skripal was considered a traitor by Moscow at the time of the spy swap. He is thought to have done serious damage to Russian spy networks in Britain and Europe.

Police believe they have identified the suspected perpetrators of the attack on Russian former spy Sergei Skripal (pictured before the attack) and his daughter Yulia (pictured after the attack) using facial recognition technology and flight manifests

Army officers in hazardous material protective suits have entered Queen Elizabeth Gardens in Salisbury to collect an item for testing

Today police were also searching the same park, where they believe Dawn and Charlie came across the Novichok in a perfume bottle

Police officers were today searching a stream which flows through Queen Elizabeth Gardens

Police remain at Mr Skripal's home, where Novichok is thought to have been smeared on the front door handle

Dawn Sturgess (left), 44, died last week, and her partner Charlie Rowley (right), 45, is fighting for life in hospital after they found the Russian nerve agent in Amesbury, near Salisbury

How Putin's GRU spy network casts a shadowy web of covert operations across globe GRU was founded in 1918 after the Bolshevik Revolution The GRU is believed by British intelligence to have been behind the Novichok attack on Sergei Skripal, who was a former colonel Russia's military intelligence until he defected to Britain. The agency, whose best known emblem is a bat hovering above a globe, was founded as the Registration Directorate in 1918 after the Bolshevik Revolution. Revolutionary Vladimir Lenin insisted on its independence from other secret services and until the fall of the Soviet Union it was subordinate to the more famous and feared KGB, the notorious internal security service. The KGB was ultimately succeeded by the FSB - the Federal Security Service of the Russian Federation run by Vladimir Putin, who a KGB officer for 16 years and later briefly the head of the FSB. According to Yuri Shvets, a one-time KGB agent, GRU officers were referred to as 'boots' - tough but unsophisticated killers. 'The GRU took its officers from the trenches,' he said, while the KGB picked its agents - including Putin - from the USSR's best universities. The GRU trains agents and then sends them abroad as military attaches in foreign embassies, according to experts. But once a member of the GRU, it is believed to be exceptionally difficult to leave. And those who do so to join foreign agencies are punished savagely. Viktor Suvorov, a GRU officer who defected to Britain in 1978, said new recruits were shown a video of a traitor from the agency being burned alive in a furnace as a warning. It is believed that GRU members are still staffing Russian embassies and using their diplomatic posts as cover to spy on host countries. That is why the Obama administration expelled 35 Russian diplomats as retaliation against the hacking of the Democratic Party just weeks before leaving office. It is also why the British government expelled 23 diplomats on March 23 following the outrage in Salisbury. The US expelled 60. Advertisement

Britain's investigation into the poisoning has taken on added urgency after Dawn Sturgess, 44, died this month having supposedly coming into contact with the same batch of Novichok four months after it was abandoned by the Russians.

Searches have been carried out Queen Elizabeth Gardens for several days with some areas of the park covered by Army experts in hazmat suits and other areas examined by police in ordinary uniforms.

It comes as an inquest opens today into the death of Dawn Sturgess (pictured), who died this month after apparently coming into contact with the same batch of Novichok

Yesterday Army experts in Hazmat suits and wearing breathing apparatus bagged up items found by a tree yesterday

It is thought the difference in clothing reflects the perceived level of risk of coming into contact with hazardous materials in different parts of the park.

The nerve agent was hidden in a perfume bottle, suggesting one of the assassins may have been a woman, and that Ms Sturgess sprayed the deadly substance onto her wrists after finding it in a park.

Her partner Charlie Rowley, 45, was left fighting for his life after also being contaminated by the chemical weapon.

It is understood mother-of-three Ms Sturgess was exposed to at least 10 times the amount of nerve agent the Skripals came into contact with.

Mr Rowley says that after finding the bottle, Ms Sturgess sprayed Novichok straight on to both of her wrists, the source said.

Investigators are working to the theory that the substance was in a discarded perfume bottle found by the couple in a park or somewhere in Salisbury city centre, most likely the park now being searched.

The Metropolitan Police, who are leading the investigation, have declined to comment on the latest claims.

But a source with knowledge of the investigation told the Press Association: 'Investigators believe they have identified the suspected perpetrators of the Novichok attack through CCTV and have cross-checked this with records of people who entered the country around that time.

'They (the investigators) are sure they (the suspects) are Russian.'

According to reports from US security officials, police have recovered grainy CCTV images of persons who inadvertently killed Dawn.

Counter-terror cops are closing in on identifying the suspects, thought to be from Mr Skripal's former employers, Russia's military intelligence service the GRU.

Police outside Mr Rowley's home in Amesbury, Wiltshire, on July 5 after he and Ms Sturgess picked up a perfume bottle containing the chemical weapon Novichok

A police officer stands guard over a cordoned off rubbish bin after Dawn Sturgess and Charlie Rowley fell ill in Amesbury

Both Mr Skripal and his daughter, as well as Detective Sergeant Nick Bailey, of Wiltshire Police, made miraculous recoveries after being on the brink of death.

All three were treated at Salisbury General Hospital, where Charlie is now being cared for.

The perfume bottle could support the theory that a woman was involved in the initial hit by up to six people against Sergei and Yulia Skripal in Salisbury on March 4.

Ms Sturgess' inquest will be opened today in Salisbury and the hearing is expected to be adjourned to allow police inquiries to continue.

On Wednesday, a fingertip search of Queen Elizabeth Gardens in Salisbury was carried out.

The park and other locations in Salisbury and nearby Amesbury were cordoned off last month after the exposure of the couple to the nerve agent.

Searches of properties could last months after 400 items were recovered, officers warned, while waste and litter will be removed as part of the sweep of public areas.

Last week counter-terrorism detectives revealed they had found a small bottle containing Novichok at Mr Rowley's home in Muggleton Road, Amesbury.

They are trying to establish where the container came from, and how it came to be in his house.

A team of international experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) was called in to independently verify this.

They have finished collecting samples which will now be analysed at two OPCW labs before the results are reported back to the UK.

Public Health England said the risk to the public remains low but it continued to 'strongly advise' not to pick up any unknown 'strange items' such as syringes, needles, cosmetics or similar objects made of materials such as metal, plastic or glass.