A woman in her 50s has died after being attacked by a dog in south London.
The victim, named locally as Barbara Williams, suffered multiple injuries during the attack on Thursday evening in Demesne Road, Wallington.
Armed police called by somebody else in the house arrived to find the woman grappling with the dog, thought to be a Belgian mastiff. It was shot dead.
Police are seeking Alex Blackburn-Smith, believed to be the dog's owner and main occupier of the house.
Det Ch Supt Guy Ferguson said he believed Mr Blackburn-Smith, 34, was already aware they wanted to talk to him.
Paramedics treated the victim, thought to be a lawyer, at the scene but she died an hour later.
A child under five years old was upstairs during the attack but came to no harm.
Police said another female lodger of a similar age to the victim was also present.
Det Ch Supt Ferguson said: "My officers were confronted with a ferocious dog which had attacked a lady in her 40s.
"They attempted to rescue her involving the use of shields and managed to contain the dog in another part of the premises."
He continued: "We urgently want to speak to Alex Blackburn-Smith to establish the facts. I think he knows of our interest."
A neighbour claimed he had raised previous concerns about the dog with both the police and Sutton Council.
The council said it had been contacted about another smaller dog from the same address in August 2009.
"At that point there were no legal grounds for the council to intervene on the basis of our statutory powers," said Councillor Colin Hall.
"There have been no subsequent complaints."
Burhan Yanbolu, a minicab driver, said: "It was always going to happen.
"We didn't have anything to do with them because of the dog.
"It was a big strong dog.
"There were two dogs and the big one would lean against the fence and could see over it on its hind legs.
"We had concerns it would get over and could get in our garden."
Police said they would look in to reports their Safer Neighbourhoods Team had received complaints over the dog.
Another neighbour, Christina Faria, 36, said: "We looked out and saw the road closed and lots of police and forensics.
"We saw a silver private ambulance take what must have been her body away."
Local business owner Pat O'Brien said: "It all went on from about 9pm to 1am before they took down the tape.
"There were about five panda cars and a crew in a car marked up as 'air ambulance'.
"I didn't see the police marksman but there was a lot of activity."
Police removed a younger dog from the home and forensics officers are now examining the house.
Belgian mastiffs are not on the dangerous dogs list.
The dogs, which can weigh up to eight stone (50kg), are said to have been used to pull carts.
The Kennel Club said Belgian mastiffs were considered extinct in the UK.
But breeds can be considered extinct if there are not enough males and females left to reproduce in effective numbers.
Some breeders are trying to reintroduce the breed by crossbreeding with similar dogs.
Police are examining the animal's remains to see if it was a pure breed.
Clarissa Baldwin, chief executive of the Dogs Trust, said the breed made a "calm, affectionate and loving pet".
She said: "The circumstances seem to be a little bit strange if it was just the family unit in the house. You call it a gentle giant."
But she added: "They can be very protective. People should give a lot of thought to the sort of dogs they are buying."