A man in his forties is due in court in Mayo later in connection with the murder of Sandra Collins 12 years ago.
The 29-year-old was last seen in Killala on December 4, 2000.
Three people have previously been arrested in connection with her disappearance, but none were charged.
Yesterday, Gardaí arrested a man in Ballina who is due before a special sitting of Ballina District court at 11am this morning.