Gardaí in Galway were still questioning two people last night in relation to the murder of Swiss school student Manuela Riedo in the city 10 days ago.
Three men and one woman were arrested under section 4 of the 1984 Criminal Justice Act as part of a planned operation early yesterday morning.
All four were in their late 20s and from Galway. Two of the men were taken to a garda station in Galway City shortly after 7am yesterday. The woman was taken to Gort Garda station. Another man was detained at about 9.30am and taken to Loughrea Garda station.
The woman and the man detained at Loughrea Garda station were released yesterday evening. Gardai said a file was being prepared for the DPP.
One of the men arrested yesterday, a 27-year-old, was being questioned in relation to the murder, while the three others were questioned about whether they withheld information in relation into the crime.
The detention period for the 27-year-old man, who was being held in Galway city, was extended for a further six hours at 1.19pm yesterday, and it was expected that it would be extended for a further 12 hours last night.
Two searches were also carried out by the Garda investigating team yesterday, headed by Supt Tom Curley of Mill Street Garda station. A number of houses and a laneway close to the Dr Mannix Road area of Salthill were searched. The Garda Water Unit carried out searches of the lake bed at Loughatalia, close to where Ms Riedo's body was found on Tuesday morning, October 9th.
Gardaí would not comment on details of the operations yesterday, but it understood that they may have been looking for clothing and for an item which may have been used as a weapon in the attack.
The postmortem showed that Ms Riedo had been strangled.
Ms Riedo (17), the only child of Hans and Arlette Riedo, was from Hinterkappeln, a suburb of Bern in Switzerland. She had been in Galway for just three days on a 14-day intensive English language course when she was assaulted and murdered.
She had been attending commercial college in Fribourg, while completing her apprenticeship in sales. She was one of a group of 43 Swiss students enrolled at three language schools in Galway and staying with different host families.
She was en route from her host family's home at Renmore Park into the city by the military walk or short-cut - parallel to the main railway line and running between Renmore and Ceannt Station in the city centre - when it is believed that she was attacked on Monday night.
She had been due to meet fellow students between 8pm and 8.30pm, but never arrived. Her body was found on an embankment the next morning.
As part of their investigation, gardaí have been analysing profiles of people involved in assaults in Galway previously. Supt Curley said last night that a substantial amount of DNA analysis had been carried out.
Supt Curley and a number of Garda officers attended a memorial service for Ms Riedo in Renmore parish church last night, on the eve of her funeral in Hinterkappeln, near Bern, today