A man has been arrested on suspicion of the murder of Lisa Dorrian in 2005.
The 25-year-old was last seen alive in the early hours of 28 Feburary in Ballyhalbert in County Down.
Police said the 68-year-old man was arrested earlier on Monday on suspicion of a number of offences, including assisting offenders, withholding information and preventing a lawful and decent burial.
He remains in custody at this time.
Nine people have been arrested on suspicion of the murder of Ms Dorrian to date.
Ms Dorrian, who was from Bangor, was last seen at 05:00 GMT on the 28 Feburary 2005, having attended a house party at a caravan park in the County Down village.
Her handbag and belongings were discovered at the party.
No one has ever been convicted over her disappearance and, despite many land and sea searches, her body has never been found.