The man who was shot dead in the Creggan area of Derry early this morning has been named as Emmett Shiels (22).
Mr Shiels was shot shortly after 1am and died soon afterwards in hospital.
A local politician said it was understood that Mr Shiels, who was from Tyrconnell Street in the Bogside in the city, was the victim of mistaken identity. Other reports suggest he may have intervened in an incident before he was killed.
A priest who went to the scene said it appeared that the victim was chased and shot by a group of masked men, possibly while delivering pizza in the area.
PSNI area commander, Chief Inspector Chris Yates, said: "This was a cold-blooded shooting." It was two hours before police attended the scene because of fears of an ambush.
Mr Robinson described the murder as a 'despicable and cowardly act'
Mr Yates insisted they had responded to the shooting within 10 minutes, knew the victim had been taken to hospital and that witnesses were at the hospital.
"The initial call was that masked men were lying in wait in the area, so under those circumstances and with the terrorist incident we have seen most recently in Fermanagh where two police officers were nearly killed, we were not going to go blindly rushing into an area until we were satisfied it was safe to do so," he said.
Northern Ireland's First and Deputy First Ministers Peter Robinson and Martin McGuinness issued a joint statement of condemnation.
"This murder in Londonderry was a despicable and cowardly act carried out by evil people," said Mr Robinson.
"There will be no turning back to the dark days of the past, we will not allow our achievements to be destroyed by violence that has no place in our society.
"My deepest sympathies are with the young man's family at this very difficult time."
Mr McGuinness added: "The people who have perpetrated this act have nothing to offer society. They do not represent anyone in Derry or in the wider community. These actions have no place in our future.
"My thoughts and prayers are with this young man's family and loved ones."
Foyle SDLP Assembly member Pat Ramsey said strong rumours in area were that the murdered man was a victim of mistaken identity.
"The word on the ground is that it was mistaken identity. Taxi drivers in the city have a great reputation for getting it right and one said to me 'They got the wrong fella'."
Mr Ramsey said he had spoken to the victim's father and the family was devastated.
"We all thought there was an end to the Troubles. For anyone, the worst nightmare is someone coming to the front door and saying your son has been shot dead".
Mr Shiels' partner is understood to be heavily pregnant.
The Foyle MLA accused dissident republicans of being responsible.
"The only people who have access to weaponry and guns of this nature are dissident republicans, the only people who have been on the war path in recent times are dissident republicans.
"There has been an increase in dissident republican paramilitary shootings and beatings in recent weeks - we have a gang who are emulating what the Provisional IRA did in the '70s and '80s with their kangaroo courts."
He said people in the area did not want the violence and those responsible needed to be marginalised by the community.
PA