Islamic State supporter Lisa Smith is set to be questioned for a number of days on suspicion of committing terrorist offences abroad.
The 38-year-old Dundalk woman was arrested as soon as she disembarked off a commercial flight from Turkey at Dublin Airport shortly before 11am.
Her two year-old daughter was given into the care of her grandparents, who she has never met before.
Experienced counter-terrorism officers took Ms Smith to Kevin Street Garda Station where she is being detained under Section 30 of the Offences Against the State Act.
A statement from Garda HQ said: “Today, Sunday 1st December 2019, at Dublin Airport, An Garda Síochána has arrested an Irish citizen (38 year old female) on suspicion of terrorist offences following her deportation from Turkey.
“She is currently being detained at a South Dublin Garda station under the provisions of Section 30 of the Offences against the State Act, 1939 as amended.
“A child, also an Irish citizen, was in the company of the female and is now being cared for by relatives.”
The provision allows for up to 48 hours detention under authorisation of a chief superintendent and can be extended for a final 24 hours on the permission of the district court.
Sources expect Ms Smith could be detained for the “full period”, at least up to 48 hours, saying the interviews will be “a slow process” and that the mother will be given full opportunity to have rest periods.
Ms Smith, a former member of the Defences Forces and convert to Islam, left for Syria in 2015 to live in the so-called Islamic State.
The Special Detective Unit, the force's counter-terrorism bureau, is conducting the interviews and it is understood senior interviewers are leading the questioning.
There was some confusion in recent weeks as to whether or not gardaí might avail of her purported willingness to voluntarily be interviewed by detectives or arrest her.
The SDU, along with Security and Intelligence at Garda Headquarters, have been involved in lengthy and regular discussions with the Director of Public Prosecutions for some time as to whether or not Ms Smith could be prosecuted under Irish laws for terrorist offences committed abroad – and consequently if they had the power to arrest her.
“There may have been a grey area during their inquiries but the fact they have arrested her means that, according to the DPP, there are strong enough grounds to arrest,” said a security source.
It is thought that the garda investigation is advanced and that the investigation team has assembled a range of evidence that they now need to put to Ms Smith to get her reply.
“The arrest suggests they have evidence gathered and want to get her side of the story, her alibis or whatever,” said a source.
Ms Smith has been talkative in various interviews she has given, both to Irish and foreign journalists, and her comments in those interviews will form part of the evidence.
It is also thought that information from foreign intelligence agencies will also be put to her.
“A lot of the evidence could be circumstantial, but we have seen in trials that that is sometimes enough for juries,” said a source.
On Saturday night, Taoiseach Leo Varadkar raised the possibility of charges being brought.
“In relation to Ms Smith, the gardaí are going to want to speak with her. They may be in a position to charge her and, if they do, prosecution may follow.”
Sources said this might indicate the strength of the garda file and the status of discussions gardaí have had with the DPP.
Depending on her responses, and if she makes any admissions, the SDU may be in a position to seek charges being brought before her detention period runs out.
In an interview last October with the Irish Examiner and RTÉ, the head of Security & Intelligence confirmed that a criminal investigation was underway in relation to Ms Smith regarding possible terrorist offences under the Criminal Justice Terrorist Offences Act 2005 and that they were “gathering evidence”.
Assistant Commissioner Michael O’Sullivan said: “We have avenues open to us where we can get evidence and how we can get that evidence and we are working with the DPP on how to put information we receive into evidence.”
He said they were confident of producing a “comprehensive file” for the DPP, who will decide if it meets the threshold for bringing a prosecution.
He recognised that the Criminal Justice Terrorist Offences Act was “untested” in relation to bringing charges for suspected offences carried out abroad.
Ms Smith and her child were accompanied on the flight from Istanbul by consular officials from the Department of Foreign Affairs and members of the elite Army Ranger Wing.
Commenting on the arrest, Justice Minister Charlie Flanagan said: “On her arrival in Dublin, Lisa Smith was met by An Garda Síochána. In the case of Ms. Smith’s child, established procedures for her care will be followed.
"This is a sensitive case and I want to reassure people that all relevant State agencies are closely involved.
“A multi-agency network is in place here comprising agency personnel who engage on an ongoing basis with international colleagues regarding emerging practice in relation to the complex issue of radicalisation. This network will coordinate engagement on a case by case basis as and when appropriate.