Mairead Philpott tells the court that as far as she was concerned her children were "in the three bedrooms".
She says she was "hysterical" at the time of the fire and does not remember getting into the ambulance or being at the hospital up until the point a doctor told her "the children had passed away".
Asked whether she was able to describe what it felt like to be told that five of her children had died, she replied: "It's like my insides had been ripped out".
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The suspect, 35-year-old Willie Corey Godbolt, has been arrested and was being treated for a gunshot wound in hospital.
Mohanna Abdhou, known as Montana, was out with friends when two attackers cycled up to them and opened fire in Brent, north-west London.
The US president tweeted that Mrs May gave him "full details" of the incident during talks while he attended summits in Europe.