The investigation into the disappearance of Fiona Pender has been reclassified as a murder investigation.
The 25-year-old woman went missing from Tullamore, Co Offaly, almost 29 years ago.
This is the first time that gardaí have described the case as a murder investigation.
To date no one has been charged in connection with Ms Pender's disappearance and her remains have never been found.
Watch: Minister tells those with information on Pender murder to come forward
Gardaí have begun searches in an area close to Killeigh, which is around 5.1km from Tullamore.
The land will be subject to excavation and a technical and forensic examination.
Gardaí expect to be in the area for a number of days.
Ms Pender was last seen at around 6am on the morning of Friday 23 August 1996 at her flat on Church Street in Tullamore.
She was 25 years old and seven months pregnant at the time she went missing, and had spent the day before her disappearance shopping for baby clothes with her mother in Tullamore.
She was said to have been in good form and was looking forward to the birth of her baby.
Ms Pender was wearing bright-coloured clothing and white leggings and was described as being 1.65m (5'5'') in height with long blonde hair.
Minister urges those with information to come forward
Minister for Justice Jim O'Callaghan has appealed to anyone who has information on her disappearance and murder to bring it to the gardaí.
Speaking in Limerick, Mr O'Callaghan said Ms Pender's family have gone through a terrible time over the last 28 years and it is incumbent on anyone who has information to come forward now.
He said gardaí had briefed him on developments in the case today.
Numerous extensive searches have taken place and several appeals for information have been made over the years.
Gardaí said that over the 28-year investigation, thousands of documents and reports have been gathered and over 300 statements have been taken.
They are continuing to appeal to anyone with any information in relation to Ms Pender's investigation and who has not spoken to gardaí, to come forward.
Similarly, they are urging anyone who may have previously come forward, but who felt they could not provide gardaí with all the information they had in relation to this matter, to contact the investigation team again.
Gardaí say that anyone with any information, no matter how small or insignificant they might believe it to be, can contact Tullamore Garda Station on 057-9327600, or any garda station.
Anyone who wishes to provide information confidentially can contact the Garda Confidential Line on 1800 666 111.
Ex-garda 'satisfied' perpetrator was known to Fiona Pender
Retired Garda Detective Alan Bailey said that he is satisfied that the perpetrator in Fiona Pender's disappearance was known to her.
Speaking on RTÉ’s Drivetime, the former national coordinator for Operation Trace said that he was confident gardaí had new information regarding the case.
"I’m certain that new information has been obtained by the investigating team," he said.
"At the outset, Operation Trace was set up to establish if we had that commonality, if there was a serial killer in operation.
"But we're satisfied, especially in Fiona's case, that the perpetrator was known to her," Mr Bailey said.
He said that there was no clear reason for Ms Pender to disappear.
"With all missing persons cases, what you're always looking for is what's referred to as a push-pull factor.
"That's some reason why somebody would leave home, maybe to form a liaison somewhere else, or are being driven out of home. In Fiona's case, from very early on it was obvious that wasn't the case.
"We never established any reason for Fiona to leave," he added.
Mr Bailey described the reclassification of the case as a "gamechanger", and said it will make a huge difference to the investigation.
"It's a complete game changer, it's something I really welcome," Mr Bailey said.
"It's something Operation Trace had recommended all along, that all of the cases of missing females that we were tasked with investigating would all be upgraded to murder.
"It makes a huge difference ... once that was upgraded to a murder instead of a missing person inquiry, gardaí then have the power to go to court, to seek warrants, to search certain areas, you have powers of arrest, you have powers to interview people," he added.
Mr Bailey encouraged anyone with information on Ms Pender’s disappearance to come forward, adding that it was not too late to present information.
