Paul Kelly is the fourth man to be shot dead in Dublin this year.
In January, Damien Dowdall (22) was shot in the head by two men who called to his home at Lealand Road, Clondalkin, while he was watching television about 10.15 pm. His partner was in the house at the time of the murder.
In February, Thomas McDonagh (28) was shot dead at St Mark's Crescent, Clondalkin.
Last month, Robbie O'Hanlon (25), originally from Arthur Griffith Park, Lucan, was shot three times by a masked gunman in the Dublin City Services Sports Club, off Coldcut Road, Clondalkin. He was leaving a soccer pitch at about 8pm when a man fired three shots from a handgun, wounding him in the head, as witnesses looked on.
Last week, Garda Commissioner Noel Conroy said that witnesses to gangland killings were refusing to testify against suspects or were leaving the witness protection programme, making convictions impossible in many cases.