A 26-year-old man has been arrested in Dublin on suspicion of the murder of 22-year-old Mary Ward in south Belfast.
Ms Ward, 22, was found dead by police at her home in Melrose Street on 1 October.
The Police Service of Northern Ireland (PSNI) has since started a murder investigation.
Assistant Chief Constable Davy Beck said the investigation was progressing at pace and police were still trying to establish the exact circumstances of Ms Ward's death.
An Garda Síochána (Irish police) said it would continue to work closely with police in Northern Ireland.
Timeline
Ms Ward died from a number of wounds to her neck, BBC News NI understands.
Her body was found by police officers who went to her house on Tuesday 1 October – but it is believed she was killed on or around 25 September.
The PSNI had been contact with her on a number of occasions in the weeks beforehand.
This began on 4 September when she made a complaint to the police about being the victim of violence.
The last contact it had with the mother-of-one was on 25 September.
Details of the murder investigation were not released until just before midnight on Monday.
It is believed the PSNI had determined a number of days ago that Ms Ward had been murdered.
Police believe Ms Ward was last seen alive on 25 September.
Police Ombudsman
Police confirmed on Tuesday that following a review of its previous engagements with Ms Ward the case had been referred to the ombudsman.
The Police Ombudsman's Office said the focus of its investigation would be on the police response to a report of violence in the weeks leading up to her death.
It confirmed the case was referred to it by police on Sunday night.
Violence against women
Head of public protection branch, Det Ch Supt Fisher, has said Ms Ward was the fourth woman to be killed in Northern Ireland in the last six weeks.
Combating violence against women and girls (VAWG) has been rising up the list of police and political priorities recently.
Two years ago, the PSNI launched an action plan.
This was followed by an Executive Office strategy published last month, external.
It is in response to the fact more than 30 women and girls have been murdered in Northern Ireland in the last five years.
In the 12 months to July, the PSNI recorded 22,400 VAWG-related offences.
The PSNI has said this is a 16% drop year-on-year and shows some progress is being made.
However, it accepts there is still much to be done by it – and wider society.