"Some people were angry, some were distressed and some just didn't want to hear anything else and, virtually, asked us to leave."

Sexual assault counsellor Lisa Waters worked with police to tell victims of serial rapist Reynhard Sinaga that they had been assaulted when they were unaware.

Sinaga, 36, was jailed for life on Monday for committing 159 sex offences, including 136 rapes.

The post graduate student was found guilty of luring 48 men from outside Manchester clubs to his flat, where he drugged and assaulted them - filming the attacks.

Lisa and her team at the St Mary's Sexual Assault Referral Centre in Manchester worked with detectives to break the news to those victims.

When many victims woke up they had no memory of what had happened.

The Crown Prosecution Service (CPS) called Sinaga "the most prolific rapist in British legal history".

Image copyright facebook Image caption Reynhard Sinaga often targeted men who were leaving clubs

Police used the videos of the assaults along with "trophies" which Sinaga had collected from the victims such as phones, watches and ID cards, to identify them.

Lisa tells Radio 1 Newsbeat why this was such an unusual case.

"Usually, when people have been sexually assaulted they know what's happened and are empowered to report it to the police or not.

"In this instance, the men involved had no idea that they had been sexually assaulted. So, they were just visited, out of the blue, by detectives to inform them."

Image caption A map of central Manchester

Lisa explains that these victims often "had to deal with two sets of of traumatic incidents" - the shock of finding out what happened to them, coupled with the trauma of the sexual assault.

And none of these men reacted in the same way.

"We had to break the news very gently. We didn't know anything about these men, we didn't know if they'd had any history of psychological harm or had been assaulted before.

"We're all individuals... I think if we start pigeonholing people and say, 'men will behave in a certain way', then we're missing an opportunity to support them in the right way."

Image copyright Greater Manchester Police Image caption Reynhard Sinaga assaulted victims in his student bedroom

Lisa says that she found the process extremely difficult on a personal level but was glad she was able to offer some support.

"Rape and sexual assault is a very isolating crime, it's difficult to process and make sense of. Just speaking to somebody and knowing that actually you're behaving in a normal way is beneficial to lots of people."

"It's very challenging and it's also it's a big responsibility to make sure that people are okay."

Greater Manchester Police said anyone who believes they might have been attacked by Sinaga can report information online or call its police line on 0800 092 0410 from inside the UK or 0207 158 0124 from abroad.

The force said anyone in need of support from specialist agencies could call 0800 056 0154 from within the UK or 0207 158 0011 from abroad.

If you have been affected by the issues raised in this article, help and support can be found at BBC Action Line.

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