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An international project featuring a rapist discussing his crime on stage has drawn both condemnation and support. So should a perpetrator be given a platform to share his experience?
"There's a rapist in the building," the protesters shouted as they briefly blocked the entrance. "Get the rapist out."
Their banners and loudspeakers were an unusual sight outside a venue better known for world-class concert performances than controversy.
The anger at London's Royal Festival Hall at the Southbank Centre on Tuesday evening was over South of Forgiveness, an event that would see a woman inviting the man who raped her to discuss the impact of his actions.
The discussion between Thordis Elva, from Iceland, and Australian Tom Stranger had already been dropped from a women's festival at the weekend following pressure from campaigners.
But it was rescheduled after organisers of the Women of the World (WOW) Festival said the debate was too important to silence.
"Rape is one of these critical issues and we need to shift the discourse around it, which too often focuses on rape survivors rather than rape perpetrators", Jude Kelly, artistic director of the Southbank Centre, said in a statement.
Diane Langford, one of the protesters waving placards on the banks of the River Thames, condemned the decision.
"I'm here because I feel a rapist is profiting from his rape," said the 75-year-old, herself a survivor of rape.
"I don't believe there can ever be impunity for a rapist."
Thordis Elva was 16 when she was raped by her then 18-year-old boyfriend, Tom Stranger, after a Christmas party in her hometown in Iceland.
After years of turmoil she decided to get in touch with him. And to her surprise, he replied with a confession and an offer of "whatever I can do".
By then it was too late for her to press criminal charges. Instead, they wrote a book together about what happened.
A TED talk they filmed last October has been watched by more the 2.7 million people and the pair have since taken part in a handful of stage appearances.
Their London fixture prompted a petition by campaigners who warned it would be a "trigger" for sexual assault survivors - bringing back painful and dangerous memories - and could "encourage the normalisation of sexual violence instead of focusing on accountability and root causes of this violence".
They said it risked "suggesting that standing on a platform alongside one's rapist is a model approach to addressing sexual violence".
The debate comes amid continued concern about the number of victims who report rape to police, both in the UK and around the world.
The BBC has previously covered cases - for example in Colombia and Myanmar- where women have been attacked and even raped again for speaking out against sexual assault.
Elva, who now lives in Sweden with her husband and son, insists she is not sharing a set of recommendations for others.
Instead, she wants to shift the focus of responsibility for sexual violence to the perpetrator rather than the victim, and bring about what she calls the "demonstrification" of attackers.
"Demonisation of perpetrators in the mainstream media got in the way of my recovery," she said.
"The fact that Tom wasn't a monster, but a person who made an awful decision, made it harder for me to see his crime for what it was."
When it was Stranger's turn to speak at the Royal Festival Hall on Tuesday, his words appeared very carefully chosen and he still seemed to have some difficulty getting them out.
"I'm not up here as some form of punishment... or searching for some kind of questionable redemption," he said.
"I'm not trying to benefit my profile or my bank balance. It would be disrespectful for me to do so."