By Sharon O’Neill
Up Close returns tonight with an investigation into the extraordinary double life of Ciaran Maxwell.
The father of one from Larne was a Royal Marine and member of the elite 40 Commando - but he was also a dissident bombmaker and quartermaster, stockpiling weaponry near his base in Taunton, Somerset and back near his childhood home in Larne.
All of this was done during most of his military career.
Tonight we ask what motivated Maxwell to do what he did, and just how did he get away with it for so long?
The scale of his hides, 43 in all, spread over eight locations, were revealed during his sentencing at the Old Bailey.
But a bomb disposal expert, who has served in Northern Ireland, Iraq and Afghanistan, has given us his assessment.
Former Colonel Gareth Powell told us what Maxwell had in his possession was a on scale he has never seen before.
He says: “This must be one of the most significant finds in the history of terrorism of Northern Ireland. He has put together almost a complete golf bag of terrorist devices.”
And that includes technology used by other extremists around the world.
“Due to the components he has and the precursors, ie the ingredients for the explosives he could produce, this man was in a position to produce a far more spectacular event than some of the ones we have seen recently,” he says.
“He has the main precursors for some of the most potent homemade explosives that we currently see in terrorism not just in the UK but globally.”
The Old Bailey was told Maxwell was building bombs for the Continuity IRA.
Asked about how he managed to evade capture for more than five years, Assistant Chief Constable Stephen Martin says: “He was very patient, he was gathering small amounts getting it from different sources to try and avoid detection.’’
On his value to dissident republicans still trying to wreck peace, he says: “I think Ciaran Maxwell unchecked would have proven to be a massive bonus to violent dissident republican groups.
"He would have been considered a jewel in the crown."
For the first time someone who knows the inner workings of that elite unit Maxwell was part of, has spoken out about the damage he has done to the reputation of the marines.
Paul Treanor was once a member of 40 Commando and has served in Northern Ireland and Iraq.
“This young lad, who organised all of this, and no-one knew about it. We are supposed to be experts in security and how on earth did this guy get away with it for such a long time,’’ he says.