A man handed himself in for questioning after his ex-wife was injured and her cousin killed in a knife attack at the couple's former home.
The victim, named locally as 32-year-old Muhammad Arif, lost his fight for life in hospital after the stabbing.
All three were originally from Pakistan and had been living in Ireland for some time. The alarm was raised shortly after 2pm on Thursday when gardai were called to an apartment in Fitzwilliam Court in Dyer Street, Drogheda, Co Louth.
Mr Arif and the woman, aged 30, were rushed to Our Lady of Lourdes Hospital in Drogheda. He was transferred to St Vincent's in Dublin where he died in the early hours of Friday morning. It had been feared his death was Ireland's first so-called honour killing, but a senior garda source said officers were treating it as a domestic incident.
It is understood the 30-year-old man in custody left his wife and their apartment about six weeks ago because of marriage difficulties. "He went back and found her with another man," the garda source said. "He got a knife and stabbed the two of them and gave himself up. This could have happened in any culture, in any place."
The woman remains in Our Lady of Lourdes but her injuries are said not to be life-threatening.
Mr Arif had been living in Ireland for several years and worked as a security guard at Tesco in the town.
A spokeswoman for Tesco said: "This case is a matter for the gardai but we do sympathise with the victim's family at this difficult time."
A friend of the victim who visited the scene said he was desperate to get in touch with Mr Arif's family back in Pakistan. He claimed the man died when a liver could not be found for an emergency transplant.
"We are all feeling very sorry," he said. "He was a security guard in Tesco in Drogheda. Most of the people here know him because everyone goes for a shop in Tesco. He's so helpful. Everyone who heard in Tesco, his colleagues, the staff, they are all feeling very sorry."