A Derry man shot dead in a city centre flat was gunned down in front of his partner.
Dissident republicans have been blamed for murdering Barry McCrory, 36, on Wednesday morning.
Police and ambulance crews attended the first-floor apartment, above business premises in Shipquay Street, close to the Diamond area of Londonderry.
Emergency services were alerted at around 11am and the scene was cordoned off.
SDLP Assembly member Pat Ramsey said people were stunned. He said: "There is a sense of bewilderment and awfulness. This happened right in the heart of the city."
The incident comes a day after Belfast man Kevin Kearney was found murdered in a lake in north Belfast.
A woman who was with the victim at the time of the shooting in Derry was taken away by paramedics in a distressed state. She was uninjured.
At one stage there were three ambulances outside the flat.
Deputy First Minister Martin McGuinness blamed dissident republicans motivated by criminal intent for the murders in Belfast and Derry, his home city.
He said: "Many of these gangs are involved in the drug trade themselves. They are routinely extorting money from drug dealers and other criminals. They are heavily involved in all sorts of organised crime. Yet they carry out murders like the ones we have witnessed in Belfast and Derry under the bogus notion that they are standing up for the community.
"The community have already made their stand. They have stood against gangsterism and criminality and stood for peace and building a new future. The community now need to work with the PSNI to bring forward information to allow them to tackle criminality and the criminal gangs who seek to profit on the backs of ordinary decent people."
Derry is the current UK City of Culture and, even though it is a major base for dissident republicans, it has been largely free of any major terrorist incidents since January.
Mr Ramsey said: "What we don't need is murderous gangs running around causing mayhem."
He said business leaders and politicians in Derry are encouraging everyone to go to the Guildhall Square to observe two minutes silence tomorrow (Friday) at 11am.
"This was an appalling and disgraceful incident which has left the city in shock. Coming at a time when things were really looking up for Derry and when people had such as sense of pride and optimism it is terrible that we are dragged back with this awful shooting.
"At the scene of the shooting today, business owners and politicians discussed giving the people of Derry a voice to express their disgust at those who are bent on destroying our unity of purpose. We also want to express our sympathies to the family of the man who has been killed.
“Business owners and politicians have agreed to come together at 11am tomorrow morning (Friday) for two minutes silence in the Guildhall Square.
“We all hope that everyone who can will come along and send a strong clear message to the perpetrators of this violent murder that it is not acceptable in our city.”
Responding to the shootings in Belfast and Londonderry, First Minister Peter Robinson said: "These murders have sent shockwaves across the community in North Belfast and Londonderry.
"They are a grim reminder of the kind of violence which the vast majority of people in Northern Ireland want to see consigned to the past.
"The rule of law is absolutely paramount and there can be no justification for anyone taking justice into their own hands.
"Anyone with information about these shootings must bring it to the police and I would hope that those responsible can be swiftly brought to justice."