Four people are being questioned about Friday night's fatal stabbing in Tipperary town.
A man in his 20s who was arrested yesterday in connection with the death of 47-year-old Willie Stokes has been released without charge.
Gardaí are appealing for the public's help after Mr Stokes, who lived in the town, was attacked in front of his 11-year-old son as they sat in their van.
Mr Stokes had never come to the attention of gardaí before and was not involved in any feud.
However, gardaí suspect he may have become an innocent victim of a increasingly savage row between Traveller families in the Waterford area.
The horse dealer was sitting in his van with his son outside a supermarket in Tipperary at 6pm on Friday evening when at least two men approached him, and then slashed and stabbed the father of four, fatally injuring him.
A murder investigation is under way, and gardaí are appealing for help from member of the public who may have seen suspicious activity in the area on Friday.
Three women and a man who were arrested in Waterford are still being questioned about the killing at garda stations in Tipperary.
The Tipperary Rural Traveller Project has said it is disgusted by Mr Stokes' death.