A man is being questioned about the shooting dead of a taxi passenger.
Detectives said a lone killer fired a number of shots into a taxi as it pulled up outside a house on Cluain Ard, Lis Na Dara, Dundalk, shortly before 4am on Sunday morning.
A 35-year-old man sitting in the back seat was hit and died. He was named locally as James Hughes, from Crossmaglen, in Co Armagh
The other occupants of the taxi, a male driver aged 48, and a 21-year-old woman in the front passenger seat, received injuries that are not believed to be life threatening.
They were taken to Our Lady of Lourdes hospital to be treated for their wounds.
A short time later a 32-year-old man presented himself at Carrickmacross Garda station, in Co Monaghan, where he was arrested. He is being held under section 50 of the Criminal Justice Act.
Sinn Fein MP for the area Conor Murphy said: "There is a very strong sense of shock and disbelief in the Crossmaglen area about the tragic killing of James Hughes.
"He was a very well known young man in the area, very well liked as well. His family is a very popular family."
Mr Murphy told the BBC: "My sympathy goes out very much to them.
"I think people are struggling to come to terms with any rationale for a very senseless killing."