The Government spent less on the State's Witness Protection Programme last year than in any year since 2011.
Department of Justice figures reveal that €800,000 was spent on the programme in 2017 compared with €1.32m in 2016.
Last year, €1.19m was alloc- ated to the scheme, but just over €400,000 of this money was not used.
The Witness Protection Programme (WPP) has caused controversy since it was introduced in the aftermath of the murder of journalist Veronica Guerin in 1996, but it remains a highly secretive scheme.
The WPP is operated by gardai and overseen by the Crime and Security Section at Garda Headquarters, supported by the Special Detective Unit and other local garda resources.
The operation of the prog-ramme and resources required for it are under continuous review.
Around €750,000 was spent each year on the WPP in 2013 and 2012; in 2010 and 2011, €700,000 was spent annually.
Operated on an ad hoc basis by the Garda Commissioner, the scheme, which has not been placed on a statutory footing, has been criticised by the Court of Criminal Appeal.
Following the failed Guerin murder trial involving convicted drug dealer John Gilligan, Judge Brian McCracken warned that the programme was badly thought-out and "one of the most worrying features is that there never seems to have actually been a programme".
Former Justice Minister Dermot Ahern also expressed concerns about the WPP in the past.
"Unfortunately, people who are targeted for witness protection, whatever it is in the Irish psyche, they don't want to leave their home, they don't want to take up their life and go to the UK or Australia and start up a new life," he said.
These sentiments were backed up in 2009 by then Director of Public Prosecutions James Hamilton, who said he felt the programme was "of limited use".
Mr Hamilton said it was a "fairly drastic" step to ask people who had witnessed a crime to move to another country and leave their families.
Among those in the WPP is David Cullen, from Tallaght, who has been giving evidence in the trial of Kevin Braney (44), also of Tallaght, who pleaded not guilty to murdering dissident republican Peter Butterly.
During the trial for the 2016 murder of Gareth Hutch (36), it was revealed that €40,000 had been spent in a year on accommodation for a key witness.
However, state witness Mary McDonnell had refused to go into the WPP.
In 2011, a Crumlin man who gave evidence against four former associates became a witness and entered the WPP along with members of his family.
A contract was put on the life of Joseph O'Brien after he gave evidence in the murder trial of John 'Champagne' Carroll.
Mr O'Brien left Ireland immediately after the trial.