Belfast City Council spent £20,000 on new security measures in response to a portrait of a former lord mayor being vandalised.
The painting of Democratic Unionist Party (DUP) peer Lord Browne was on display inside Belfast City Hall when it was damaged in October last year.
A Sinn Féin employee at Stormont later resigned over the incident, which is being investigated by police as a hate crime.
The spending was revealed to BBC News NI following a complaint to the information watchdog after the council had declined to disclose the figure.
Officials argued the cost could not be published due to an "active police investigation".
But following a complaint to the Information Commissioner's Office (ICO), the council confirmed it spent £20,000.
A council spokesman said: "A review of general security arrangements was undertaken following this incident, and a number of improvements were made."
No details were given on the nature of the new measures, but images appear to show a new security camera installed near the portrait.
The cost is on top of the almost £2,500 spent on repairs to the painting, which were carried out by a professional conservator.
DUP councillor Dean McCullough said the incident last year was "deeply concerning" and questions over what happened "are not going away".
He said City Hall is a "shared space" and the unionist community "deserve the same respect as anyone else".
"So all we are asking for is answers, accountability and justice, which is right in any democratic society," he added.
The painting was damaged following an event at City Hall to celebrate an Irish-language group's 20th anniversary.
Glór na Móna said it was "extremely disappointed" to learn of the incident and would assist the council with its enquiries.
The Police Service of Northern Ireland (PSNI) said it was treating the portrait damage as a "hate crime".
A man attended a voluntary police interview in November last year.
And in March this year, a file reporting a suspect for alleged criminal damage was sent to the Public Prosecution Service (PPS) for consideration.
The incident came just days after a decision to remove former Sinn Féin lord mayor Niall Ó Donnghaile's portrait from City Hall.
It followed controversy after it emerged Mr Ó Donnghaile had quit the party over sending inappropriate texts to a teenager.
A council spokesman said it was able to confirm the costs of new security improvements "as they are not directly related to the PSNI investigation" concerning damage to Lord Browne's portrait.
The spokesman added: "We can also confirm that council has paid for the repairs to the portrait, pending the outcome of the PSNI investigation, but will seek to recover these costs."