An investigation has started into the death in Holloway prison of a woman who was the victim of police brutality in 2012.
Sarah Reed, 32, was found unresponsive in her cell at Holloway prison at 8am on 11 January, the Ministry of Justice told BuzzFeed News.
Holloway prison staff "attempted CPR, but she was pronounced dead shortly after", the ministry said.
Reed was being held at Holloway over an incident at a south London hospital, The Guardian reported.
News of her death provoked outrage on Twitter and other social media sites on Wednesday. BuzzFeed News understands that Reed had a history of mental illness.
Civil rights activist Lee Jasper, who published details of Reed's death on his blog, told BuzzFeed News "a number of key questions need to be answered".
The MOJ has not yet confirmed any details of how she died, and relatives have claimed they were not allowed to see Reed's body during a visit to the prison, which justice secretary Michael Gove has earmarked for closure.
A spokesperson for the Prisons and Probation Ombudsman confirmed to BuzzFeed News that an investigation into Reed's death is underway.
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CCTV footage of Kiddie's attack on Sarah Reed was shown at his trial.
In 2012, Reed was punched and pinned to the ground by a Met police officer after being suspected of shoplifting at a clothing store in Regent Street, central London, the BBC reported.
CCTV footage showed PC James Kiddie pushing Reed, grabbing her by the hair, and punching her as she lay on the floor.
In 2014, Kiddie was found guilty of common assault and was dismissed without notice.
He had previously been the subject of two substantiated complaints – for lack of courtesy and respect in 2008, and for discriminatory comments in 2011.