Specialist garda child interviewers are waiting to speak to an 11-year-old boy who saw his father shot dead in a gang-related attack in Dublin last night.
Declan O'Reilly, 32, was killed while walking with his son on the South Circular Road.
Gardaí believe that two men - a gunman wearing dark clothes and a balaclava, and a driver - were involved in his murder.
In a separate incident hours earlier, 27-year-old Gerard Eglington was shot and killed in front of two children - his son and step-daughter - at his home in Co Laois.
Taoiseach Enda Kenny and Minister for Justice Alan Shatter have condemned the killings.
Deputy Garda Commissioner Nacie Rice described the murders as acts of depravity.
A senior garda has said the force is determined to bring to justice those responsible for the murders.
Mr O'Reilly was hit in the upper body and neck after a gunman got out of a silver BMW and shot at him at least four times.
He was pronounced dead on arrival at St James's Hospital.
The car used in the shooting was found burned out a short time later at nearby O'Curry Avenue. A gun was found in the car.
Gardaí are appealing for witnesses or anyone with information to contact them at Kevin Street Garda Station.
Mr O'Reilly had survived a previous attempt on his life just over a year ago when he was shot at least three times in the chest and arm in a laneway near a school off Harold's Cross Road.
He had been aware that his life was in danger. In 2007, he stabbed and killed drug dealer Derek Glennon in prison.
He was tried but found not guilty of murder or manslaughter. However, he remained under threat from the criminal gang that Glennon was involved with.
Earlier, Alan Shatter described the murders as barbaric, and said the killings showed that the gunmen had absolutely no respect for human life.
Mr Shatter said the callousness of the perpetrators showed that they lacked even a shred of humanity or decency.
He said that from discussions with gardaí, he was confident that they would continue to "bear down heavily on the activities of those involved in gangland crime".
Fianna Fáil has called on the Justice Committee of the Oireachtas to hold a special hearing on recent killings.
Justice spokesman Niall Collins suggested that Garda Commissioner Martin Callinan should also attend the special session.
Mr Collins said there was a fear that a sinister criminal element no longer feared the rule of law.
He said they were prepared to commit the most violent of crimes at any time of the day or night with no regard for the safety of communities.
Deputy Garda Commissioner Nacie Rice said that while violent crime was once again on the increase, gardaí would do all they can to bring the perpetrators to justice.
However, the association representing garda sergeants and inspectors has criticised the cuts in garda numbers and budgets, and it warned Minister Shatter against any further cutbacks.