WELSH police say that the next 24 hours are "critical" in the search for missing Irish woman Catherine Gowing .
Police today sought more time in order to further question a 46-year-old man suspected of murdering her.
Detectives were due to submit a court order this morning as their investigation enters its most "critical period yet".
The investigation into the disappearance of the County Offaly vet has now entered its fourth day -- with hope fading that she will be found alive.
Catherine has not been seen since she left her workplace in the northern Welsh town of Mold on Friday evening.
Police now suspect that she was murdered.
Officers probing her disappearance are desperate to locate her Renault Clio -- which they say could be crucial to the investigation.
"At this point finding the car she was driving could be key," a source said this morning.
"It's absolutely vital to the investigation.
"The next 24-hours could be the most critical yet, but at the moment all lines of enquiry are being closely examined."
Catherine's family have been left devastated by her disappearance and have lost virtually all hope that she will be found alive.
"They are just numb. She was everything to them. Her entire family is just inconsolable," a family friend told the Herald.
Detectives were today scouring the veterinary clinic where Catherine worked in a bid to identity any clues.
They were also questioning a 46-year-old man -- known to the Offaly woman -- at a local police station today.
Catherine's flatmate, Jane Doyle was in Ireland over the weekend and has now returned to Wales.
Catherine's heartbroken sister Emma and brother-in-law Shay released a poignant statement describing her as "the light of our lives".
"The family are devastated with the news and will try and come to terms with Catherine's disappearance.
"She is the light of our family and we can't imagine that light's gone," she said.
Catherine, originally from Clonlee, Co Offaly, was last seen at about 7pm leaving Evans Veterinary practice in Mold.
Det Supt Hanson, who is leading the investigation, emphasised the importance of locating the miss vehicle.
"Initial enquiries by police officers have resulted in the identification of a 46-year-old Gwynedd man who frequents the New Brighton area and is known to Catherine.
"This man has now been arrested on suspicion of her murder and he is currently being questioned at a local police station.
"The information which led us to arrest him forms part of our investigative strategy and it would be inappropriate for me to elaborate further at this time."