Gardaí arrested a man yesterday in connection with the fatal shooting of a 22-year-old man in Clondalkin, Dublin, last January.
They also arrested three other men in relation to what officers described as other "serious crimes", including firearms offences, in the Clondalkin area.
Damien Dowdall, a printer, was the first person to die as a result of a gun attack last year.
He was shot by two men who called to his home on Lealand Road, Clondalkin, while he was watching television with his girlfriend on the night of January 23rd last. He had no criminal convictions and was not known to gardaí.
A Garda spokesman said a 23-year-old man, who is from the Clondalkin area, was arrested "as a result of the ongoing investigations into the murder of Damien Dowdall".
He was being held at Clondalkin Garda station under Section 30 of the Offences Against the State Act, where he can be held for questioning for up to 72 hours.
Two of the three other men who were arrested are aged 19, while the third man is 33. They were being detained at Clondalkin and Ballyfermot Garda stations last night.
Mr Dowdall was watching television with his girlfriend, Debbie Quinn, at their home when two armed and masked men called to the house. When Ms Quinn answered the door, they pushed past her into the hallway. They then ran into the sitting room, singled out Mr Dowdall and fired two shots from a shotgun. The victim was hit at least once in the head. Both attackers fled the scene on foot.
Ms Quinn was the only other person in the house at the time of the killing.
Gardaí said at the time that Mr Dowdall's parents, Carol and Damien snr, knew of no reason why he would be targeted.