A Royal Marine who led a double life as terrorist bomb-maker could have evaded justice if he not been caught up in an unrelated assault case, a senior detective has revealed.
Ciaran Maxwell's suspected involvement in the violent incident led to his DNA being stored on the national database even though he was not prosecuted, and that was how detectives investigating mysterious arms dumps in Northern Ireland linked them to a serving Royal Marine in England.
It was not the only piece of good fortune that led to Maxwell's terror plans being foiled.
Police say the first two of his 43 weapons hides were discovered by accident in forest parks in Co Antrim - one by a dog walker, the other by a camper.
Senior investigating officer Gillian Kearney, a detective chief inspector with the Police Service of Northern Ireland (PSNI), said: "I have no doubt the action of the public in this case has saved lives."
DCI Kearney outlined how DNA traces found on some of the weapons were linked to Maxwell.
"He had been involved in an assault previously and his DNA was on the national DNA database," she said.
How a terrorist managed to infiltrate the British military has raised questions around the vetting process of the Royal Marines.
While Maxwell now faces 18 years behind bars, police fear weapons he constructed may still be in circulation, ready for deployment by dissident republicans.
Four of his pipe bombs have already been used by the violent extremists in Northern Ireland - two detonated, without causing injury - but detectives acknowledge others might still be out there.
PSNI Assistant Chief Constable Stephen Martin said: "We are quite clear Ciaran Maxwell had a link to a violent dissident republican group in Northern Ireland.
"There is a strong likelihood that items associated with Maxwell have made their way into the hands of violent dissident groups in Northern Ireland and four of those items have been used, three in the last year.
"There is no doubt that he knew these items were going to be used by violent dissident republican groupings."
Detectives believe he essentially operated as a lone wolf, who despite links to the Continuity IRA, acted largely independently of that renegade organisation.
Commander Dean Hayden, of the Met's Counter Terrorism Command, said: "There is no evidence to suggest Maxwell himself was directly involved in the deployment of the items but he was the bomb maker.
"A significant number of dangerous items were prevented from getting into the hands of terrorists, hence the public relationship in fighting terrorism is crucial."
Maxwell denied he joined the Royal Marines with the intention of infiltrating them from the outset, insisting his criminal exploits only started when his friendship deepened with an old acquaintance who was in the Continuity IRA.
He claimed things then spiralled out of control and, as his lawyer put it, he got "in above his head".
But detectives are not convinced by this explanation.
DCI Kearney said: "It's hard to say - we don't know that definitely.
"Whatever his motivation was in joining the Royal Marines, quickly he became involved in the engineering of devices and very dangerous activity which made him a very dangerous individual."
The lead detective said Maxwell used his military know-how to accumulate and construct the devices.
"This was reflected in how methodical and organised he was in the way he stockpiled these things," she said.
"It also gave him access to munitions and items that he could use to help him stockpile and further his activities.
"I think this is very unusual and it is certainly the first case of its kind in recent years."
Over five years, Maxwell, 31, stockpiled mortars, anti-personnel mines, pipe bombs, ammunition and handguns in hides as well as an image of an adapted PSNI pass card and uniform.
He wrote a "to do" list on which he identified over 300 targets, including police and military buildings as well as named individuals in Northern Ireland and Britain.
Maxwell joined up in September 2010 as a signaller and moved on to 40 Commando at Norton Manor Camp in Somerset in 2013, where he not only stole his colleagues' credit card details, but also a large amount of ammunition.
He was about to be promoted to corporal when his double life was exposed.
His efforts to build bombs began in 2011 and he sourced information and many of the components he needed from the internet.
Terrorist documents and bomb-making guides, including the Irish Republican Army "Green Book", were found on Maxwell's media devices, along with potential targets.
The Old Bailey heard he did a lot of his construction work while on leave in Northern Ireland in the home of his late grandmother.
The finds in two parks near Maxwell's home town of Larne initially perplexed detectives.
While they bore all the hallmarks of a dissident republican stash, the locations did not quite add up.
Larne is a staunchly loyalist/unionist town and the last place one might expect to find a dissident arms dump.
Maxwell grew up in Larne's small minority Catholic community and claimed he suffered sectarianism throughout his early life.
In 2002, aged 16, he was subject to a brutal beating at the hands of loyalists - a separate incident to the one that resulted in his DNA being added to the database.
While he claimed that left him dealing with post traumatic stress disorder, he denied it pushed him into adopting hard-line republican sympathies.
His support for violent republicanism, he claimed, was fake - motivated by fear of dissidents who knew he was British serviceman.
The discoveries at Carnfunnock and Capanagh forest parks last year sparked a major operation involving the Counter Terrorism Command (SO15), the South West Counter Terrorism Unit and PSNI.
In August 2016, Maxwell was arrested at his base and a search of Powderham plantation in Devon revealed more weapons stashes.
The hides, near his home of Exminster, contained more improvised explosive devices, chemicals, tools, electronic storage devices, hand-written notes and a small cannabis factory.
He used the drugs to supplement his military income and had copies of bank cards stolen from his comrades to be used in a fraud.
In total, police recovered 14 completed pipe bombs, two anti-personnel mines, two explosively formed projectiles (EFPs), 29 firing systems, 33 bomb initiators, two hands guns and a large amount of ammunition.
They seized components for many more explosive devices as well as over 100kg of explosives in Northern Ireland and a smaller quantity in the south west of England.