A Tulse Hill man, serving a nine-year prison sentence for manslaughter, has been using Facebook to post photos of himself from his prison cell.
Demetre Fogo, of Purser House, Tulse Hill, was convicted last year of manslaughter and conspiracy to rob in relation to the killing of 21-year-old Anthony Ogazi.
Mr Ogazi was set upon by a group of young men and stabbed to death in May 2008.
The Facebook page, which has now been removed, showed Fogo posing in his prison and flexing his muscles.
Rosie Ogazi, Mr Ogazi's sister, said she was worried that the men involved in her brother's death could access sites such as Facebook.
She said: "I live in the same vicinity as them and knowing they have access to the outside world is a bit scary.
"I thought I wouldn't have to deal with them until they were up for parole.
"To think they get mobile phone access to Facebook is ridiculous.
"If you take away someone's life then so far as I am concerned you are only entitled to basic human rights like air, food and water. This seems more like a youth club than a prison."
The discovery follows a high profile campaign by Justice Secretary Jack Straw to crack down on the use of Facebook pages by prisoners.
Although prisoners are not given access to social networking sites, they have been able to create and update Facebook accounts through outside contacts and by using mobile phones.
In some cases they are using the sites to taunt their victims.
Mr Straw said: "We have already strengthened the law to make it a specific criminal offence to bring mobile phones and their component parts into or out of a prison.
"We are also legislating to introduce an additional criminal offence for the possession of a mobile phone within a prison without authorisation."
He added: "We will not hesitate to use existing law to tackle those cases where offenders seek to taunt or harass victims and their families."
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