A man arrested in connection with the fatal stabbing of Dean Fitzpatrick in Dublin at the weekend has been released from custody without charge.
A Garda spokesman said a file was being prepared for the Director of Public Prosecutions.
Mr Fitzpatrick (23) is the brother of Amy Fitzpatrick, who went missing in Spain in 2008 at the age of 15. He and his sister were their mother Audrey's and father Christopher's only children.
The suspect, who is in his early 40s, presented himself to gardaí for questioning early yesterday, about 12 hours after Mr Fitzpatrick had been fatally stabbed at 11.20pm on Saturday at the Burnell Square apartments, Northern Cross, Malahide Road, Dublin.
Mr Fitzpatrick was rushed to Beaumont Hospital but pronounced dead soon after. The apartment he had been in and an area outside it was sealed off for a forensic examination.
The dead man had been stabbed in the abdomen. Gardaí in Coolock have appealed for information.
The Fitzpatrick family is well known, having run a campaign for the past 5½ years in an effort to progress the search for Amy. They had met former taoiseach Brian Cowen and lobbied Taoiseach Enda Kenny.
Amy and Dean went to live in Spain in 2004 and were living there with their mother and her partner, Dave Mahon, when Amy went missing.
She was last seen walking home from a friend’s house near Mijas on the Costa del Sol at about 10pm on New Year’s Day 2008.