A dog which mauled five police officers during a raid in east London is thought to have been responsible for another attack last year.
However Scotland Yard admitted it failed to pick up on intelligence that the "pit bull-type" animal lived at the property in Albert Square in Newham before they stormed the address.
One constable is facing skin grafts on his body and all five officers needed hospital treatment for leg and hand wounds after the frenzied assault. They are all in a stable condition, but at least three will stay in overnight.
The dog was shot dead at the scene by a marksman from the Metropolitan Police's CO19 firearms unit and its owner, a man in his 20s, was arrested by bloodied officers for grievous bodily harm and kidnapping.
Newham Council said it had launched an investigation last year after receiving a complaint that a dog had bitten a cyclist in the square in April 2011. Animal welfare officers visited the property on May 6, but there was no response and the matter was discussed with the police in June with no further action taken.
A neighbour described how one officer leapt on to the bonnet of a car to escape the crazed brown dog, as the raid quickly turned into a savage attack.
Dennis Clarke said: "The dog was holding on to his leg. He managed to get to the wall but the dog got over the wall and was trying to attack him again. He scrambled on to the car, stayed there for a minute. He got down when another officer was screaming and yelling."
The incident came as more than 1,000 people were arrested over 48 hours during a massive police operation to round up wanted suspects, Scotland Yard said.
Hundreds of officers made more than 1,800 "visits" across London over two days during efforts to hunt down people wanted for questioning or who had failed to appear in court.
The operation - codenamed Big Wing - focused on suspects who failed to attend court charged with grievous bodily harm, robbery, burglary, domestic violence or had breached prison licence terms. Police said the final total of arrests was 1,065 over the two days.