The case represents the culmination of Operation ARBACIA, which was launched nearly a decade ago against dissident Irish republicans by MI5 in collaboration with the Police Service of Northern Ireland. The case centers on the evidence provided by Dennis McFadden, who has just been identified as a key witness for the prosecution. It has been reported that McFadden, born in Scotland, was a police officer before he joined MI5. He spent two decades as an MI5 officer, much of that undercover.

At first, McFadden joined Sinn Féin, which is widely considered to have operated as the political wing of the Provisional IRA (PIRA). From the late 1960s until 2005, the PIRA waged an armed campaign for the reunification of British-ruled Northern Ireland with the Republic of Ireland. Following the dissolution of the Provisional IRA, McFadden kept contact with dissident Irish republicans, a term used to identify those who disagreed with the Provisional IRA’s decision to end its armed campaign. McFadden joined the New IRA as soon as it was founded in 2012.

Gradually, McFadden rose through the ranks of the New IRA until he joined the group’s high command. This gave him access to the New IRA’s network of safe houses in Northern Ireland and Scotland. Many of these locations were eventually bugged by MI5, and the information acquired from these bugs is expected to be used as evidence in the trial of the New IRA’s leaders next year. Ten people —almost all in their 40s and early 50s— have been arrested as part of Operation ARBACIA. They include a 62-year-old Palestinian doctor who lives in the United Kingdom, who is accused of having participated in the preparation of terrorist acts. Some observers have also stated that the court will be hearing evidence connecting the New IRA with Arab militant groups in the Middle East.

The MI5 moved McFadden out of Northern Ireland last summer, just as the Real IRA suspects were arrested by authorities in a series of coordinated raids. He is believed to be living in a secret location under police protection. Meanwhile, the 10 suspects are being held in Maghaberry prison, a high-security complex in Lisburn, a city located a few miles southwest of Belfast.