Researchers say the nerve gas used in the poisoning of former Russian spy Sergei Skripal and his daughter, yulia, is likely to be supplied by a state.
The attack was seen as an attempt to murder, but it was not clear what type of nerve gas or who had used it.
Sky news has spoken to two experts who believe it is a professional.
“These compounds are very toxic,” said Andrea Sella, a chemical weapons expert at university college London. “the only place they really are likely to come from is the national laboratory.”
“You need a certain level of skill, which is very important to do that.
“The funny thing is, when amber ruder talked about the attack, she talked about it as shameless – no doubt – but I don’t think it was reckless.
“This is very specific, it does suggest that the personal bad message to a particular the guilty is not the degree of punishment, and said that we can make what we want at any time anywhere.
“The choice of the neural media really narrowed it down to state actors.”
Antiterrorism expert Andy Oppenheimer told sky news that all possible compounds “are part of a chemical used specifically for warfare”.
“These specific nerve agents are highly toxic and require specialized knowledge to produce them,” he explained.
“You need a proper military laboratory, you need the maximum protection, and who is responsible for these terrible attacks, who has to protect themselves.
If it is through a spray, or if it is directly on the skin or inhaled, it must be completed quickly so that they can escape.
“So yes – they may be well trained, unlike the amateur attackers who we think are responsible for VX attacks at Malaysian airports.
“It looks like a professional game.”
But there is an argument against state-sponsored theory.
Alexander vasiriev, a Russian spy historian and journalist, believes that “every possibility should be properly investigated”.
He told sky news: “from the professional perspective of former KGB officers, I think it makes no sense to kill someone in most situations.
“It usually has a lot of unintended consequences, as in the litvinenko case, where the damage is usually done by the person, so it makes no sense to kill him.
“It seemed to me like a Mafia thing, and after he moved to England, I would look into sergey’s business dealings.
“In the 1990s, Russian businessmen killed each other, but then they moved to Europe, including the UK, and they changed their geography, but their approach did not change.
“Another possibility is that putin was framed by his political opponents.”
Another problem is determining the type of nerve gas used in the attack.
VX is an extremely toxic compound originally developed for military use.
Just 10 milligrams of VX can absorb enough skin to cause a “fatal nervous breakdown” within 15 minutes.
It is a clear colorless liquid that is difficult to detect.
VX penetrates the skin and destroys the transmission of nerve impulses. Those exposed to agents experience convulsions, loss of consciousness, paralysis and fatal respiratory failure.
It is believed to be the material of the half-brother, Kim jong UN, who stabbed Kim jong UN at the airport in Kuala Lumpur, Malaysia, on February 13 last year.