The 'most prolific rapist' in UK history was known by his friends as bubbly and cheerful

Joshua Bote | USA TODAY

Show Caption Hide Caption Notorious British rapist sentenced to life in prison Britain’s worst rapist sentenced to life in prison. A previous version of this video mistakenly identified the citizenship of Sinaga, who is Indonesian.

Before a two-year investigation led to a life sentence in prison Monday, the man British prosecutors described as “the most prolific rapist in British legal history” was known by his victims as a Good Samaritan and by his friends as a cheerful man.

Reynhard Sinaga, a PhD student from Indonesia living in Manchester, was convicted of 136 rapes and sexual offenses on 48 men, though police believe that he may have had at least 195 victims based on films found on his phone – and other paraphernalia he kept of his “conquests.”

Prosecutors said Sinaga introduced himself to young men outside night clubs; Factory, a nightclub by his apartment, was often his destination, reported the Guardian. He offered them a place to stay for the night, as many were intoxicated, while others had lost their cellphones or their credit cards, per Reuters.

'Prolific rapist': Reynhard Sinaga, convicted of abusing 48 men, gets life in prison

Government prosecutor Ian Rushton said most of his victims initially thanked Sinaga for offering them accommodation. Some were unaware of his attacks until several years after they took place, per the Guardian.

But the Guardian reported that once Sinaga took these men home, they would totally black out until the next morning. It is unclear what substances Sinaga used to drug the men, as investigators did not find any evidence at his home. Prosecutors, per Reuters, suspected he used the common date rape drug gamma-hydroxybutyric acid, known as GHB.

Among his circle of friends with whom he frequently went clubbing in Manchester’s LGBT neighborhood, his horrific crimes were met with shock, reported the Guardian. He was known as cheerful and giggly, and was known to go out most days of the week.

One friend, per the Guardian, said Sinaga had a tendency of displaying erratic behavior after being rejected. Following a breakup, she said, he threatened to drink bleach.

A hotline opened by Manchester police following Sinaga's sentencing may reveal more of his victims, the Guardian reported. He will serve a minimum of 30 years in prison.

Contributing: The Associated Press. Follow Joshua Bote on Twitter: @joshua_bote