A 21-year-old man has been detained in Glasgow in connection with the disappearance of Karen Buckley.
Police divers, a helicopter crew and search dogs have been searching Dawsholm Park, where the 24-year-old's handbag was found.
Police have now sealed off two new scenes as they continue their search for the Cork woman.
A large number of police vehicles have arrived at Craigton farm, where a significant media presence has gathered.
And about 3 miles away Police have closed off a road near the Windyhill golf club, in the Bearsden area of Glasgow, where the police helicopter has been spotted overhead.
The Irish student vanished in the early hours of Sunday after spending Saturday night with friends at Glasgow's Sanctuary nightclub on Dumbarton Road.
She told them at around 1am she was going to the toilet, but failed to return and left her jacket behind.
CCTV spotted her leaving the club with 21-year-old Alexander Pacteau, who then drove her to his flat in Dorchester Avenue.
21 year old man arrested in #Glasgow as police seal off new area north of city at Windyhill golf club. #KarenBuckley pic.twitter.com/BkaPItkIxn
— Juliette Gash (@JuGashTodayFM) April 15, 2015
Forensic specialists and the police search unit have focused their investigation on 3 main areas – concentrating mainly on the house and vicinity where Karen Buckley’s whereabouts were last recorded – on Dorchester Avenue at the home of 21 year old Alexander Pacteau who is assisting police with their enquiries but is not being treated as a suspect.
The second place, the location where Karen’s bag was found less than half a mile away at the Dawsholm industrial park in the Kelvinside area of the city - bordered by both the River Kelvin and the Forth and Clyde Canal.
Locals say it would not be normal for any woman to venture into the Dawslholm park alone, in the middle of the night.
Police are also keen to find out more about a grey car that was seen on the roads between Milngavie and Drymen north of Glasgow between 11:00 and 15:00 on Monday.
These locals spoke to Newstalk.com about the area.
Her parents, who have flown from Cork to help with the search, said it was typical for her not to use taxis.
Ms Buckley spent Saturday night with friends at Glasgow's Sanctuary nightclub on Dumbarton Road.
She told them at around 1am she was going to the toilet, but failed to return and left her jacket behind.
CCTV spotted her leaving the club with Mr Pacteau, who then drove her to his flat.
Detective Superintendent Jim Kerr said: "He believes he was intimate with her at his flat consensually in the early hours of Sunday."
"From what we can see, she does not appear to be under duress, there's no signs of a struggle or reluctance on her part to leave the club."
Police say they are now "gravely concerned" for the student's wellbeing.
"Please return her"
The parents of Ms Buckley, who studies occupational therapy and is originally from Cork, said they were "desperate" for the public's help.
"We just want Karen home safely, we are desperate. She is our only daughter, we love her dearly," said her mother, Marian.
"If anybody has any information please come forward, we would dearly appreciate it."
Ms Buckley's father, John, said: "If anybody is holding Karen, if anybody knows anything of her, please return her. Please let's have her back. We love her to bits."
The Scottish First Minister, Nicola Sturgeon, is hoping for a positive outcome.
Det Supt Kerr said Ms Buckley was widely travelled and was "aware of how to take care of herself".
Police also want to find out more about a grey car seen on the roads between Milngavie and Drymen, north of Glasgow, between 11am and 3pm on Monday.
Det Supt Kerr said: "The activity of this grey car on the Monday is something that we're a wee bit concerned about. This car has been seen at various locations on these roads and I want to know why."
Newstalk.com's Shona Murray, who is in Glasgow, told Lunchtime there has been renewed activity in and around the house where Karen apparently spent a number of hours after leaving the nightclub.
