Mr O'Neill, who was in Spain with his family for a friend's wedding, was shot following an altercation at a bar in the resort of Benalmadena.
Mr O'Neill's family said yesterday he was not involved in the row and died because he got in the way of the gunfire.
It is understood the suspect is wanted in Britain in connection with a kidnapping.
He is believed to have fled the resort with his wife immediately after the shooting.
