Gardai have released without charge a civil servant who was arrested in relation to alleged irregularities in the issuing of residence visas for foreign nationals.
The 31-year-old man was arrested under Section 4 of the Criminal Justice Act, 1984 in north Dublin on Friday morning and was taken to Harcourt Street Garda Station for questioning.
He was released later that night.
A Garda spokesman said the arrest was just one part of "a huge investigation" which began last year. The inquiry centres on alleged corruption in the renewal of residence visas for foreign nationals attending English-language schools in the Republic.
Gardaí are investigating the reported acceptance of false school attendance certificates from up to five schools. One of these schools closed last December with 250 students on its register.
The school's administrator, a Chinese woman, has since gone missing and is believed to have returned to China. Students claimed the woman brought them to the Aliens Registration Office, where, they claimed, they were able to skip queues and have their residence permits renewed for a fee of up to €1,270.
Gardaí are investigating five other schools which are suspected of supplying students with fake attendance certificates. These are needed by students from outside the European Economic Area for the renewal of residence permits.
The schools at the centre of the investigation are believed to target predominantly Chinese and Russian students.
Gardaí were said to be monitoring a number of other foreign language schools to ensure regulations on facilities and class sizes were being adhered to. One school was estimated to have 2,000 students but only two classrooms.
Of the estimated 200,000 foreign students in Ireland, 80 per cent attend recognised colleges, according to the Academic Council for English Language Schools, which has overall authority for the sector.