A 62-year-old man arrested on suspicion of the murder of 26-year-old Annie McCarrick has been released without charge.
The businessman was questioned for 24 hours over the past two days.
Gardaí are continuing to search for human remains.
A cadaver dog has been brought in to search a house in Clondalkin in Dublin, which has been sealed off for the past two days.
Watch: Cadaver dog arrives on site during the search in Clondalkin
The specialist dog, which is on loan from the PSNI, searches for human remains and has been introduced as part of the search of parts of the house, the front driveway and the 100ft back garden.
Gardaí have also been using heavy equipment, a mini digger, a concrete saw and a kango hammer to excavate in the search for evidence in the murder investigation.
Gardaí say the current residents are not connected in any way with Ms McCarrick or her disappearance.
Ms McCarrick went missing in Dublin over 32 years ago.
The American woman had been due to have dinner with friends at her apartment in Sandymount that weekend but they became concerned when they had not heard from her, she had not turned up for work and was not at home.
Her last confirmed activity was just after 11am on Friday, 26 March 1993, when she bought groceries which were discovered unpacked in her home two days later.
Her friend reported Annie McCarrick missing that Sunday evening, 28 March 1993.
The 62-year-old man arrested yesterday morning on suspicion of murder by detectives from the Serious Crime Unit in Irishtown was released from a Dublin garda station this afternoon.
The businessman, whose home in Co Meath has also been searched, knew Annie McCarrick in the 1990s and is described by gardaí as an associate who moved in her circle.
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Read more: McCarrick lawyer hopeful case will be solved one day
Gardaí say they are keeping an open mind as to whether today's search will yield anything and point out that the introduction of a cadaver dog is part of the process in cases like these.
The same dog was used in the searches for both Tina Satchwell and Mike Gaine and while he discovered Ms Satchwell's remains, he gave no indication of anything during the search of Mr Gaine's farm.
The search at the Clondalkin house is expected to continue for a number of days.
