Police tasered and arrested a man yesterday after the body of a 20-year-old woman was found at a house in a Newry housing estate.
Police are treating the woman's death as suspicious.
Grainy images showed PSNI officers detaining a 23-year-old man in the Dromalane Park estate, close to the Newry canal.
Councillor Gavin Malone said local people had told him the man police arrested had been running through nearby gardens.
The councillor described the small community as having been "devastated" by what had happened
He said: "I was at the scene for two hours as the situation developed. People are in shock. It's desperate.
"When I arrived, there was a large police presence in the area, with a search under way for the suspect.
"They caught up with him very close to the house, and he was tasered and arrested.
"Local people are devastated and saddened.
"Very, very sad."
The authorities have not released the identities of either the suspect or the victim, but the PSNI said they were not looking for anyone else in connection with the woman's death.
The two young people had kept themselves to themselves since moving into the house, Councillor Malone said.
"No-one really knew them."
Honorary Polish Consul in Northern Ireland Jerome Mullen confirmed that both the man arrested and the woman who died were Polish nationals.
A large part of the Dromalane housing estate was sealed off yesterday as police searched the area.
Residents were asked to stay in their homes and lock their doors and windows until the police located the individual they were searching for.
Gerry Coyle of the Dromalane/Quays Community Association said the police had arrived at around 8.30am accompanied by an ambulance.
Shortly afterwards, more police officers and detectives arrived. He said: "That raised people's suspicions that something serious had happened."
Mr Coyle - who lives close to the house where the woman's body was discovered - added: "The forensic teams will be there until today (Monday) and people are advised to keep away from the area. The only people who will be allowed there will be the people who live within that part of Dromalane park.
"The community is shocked and traumatised by what's happened but more importantly they're heartbroken. We didn't know the young girl that well, she was only here about six months.
"But traumatised would be an understatement.
"We're heartbroken at what has happened."
Local residents last night laid floral tributes in memory of the young woman who died.
Newry and Armagh MP Mickey Brady urged anyone with information about the death to contact the police.