For 2½ years, the young Indonesian man named as Britain's worst rapist prowled the bars and restaurants of Manchester in search of young male victims.

Reynhard Sinaga, 36, lived just a few doors away from the popular Factory nightclub, on Princess Street in central Manchester, and the club became his favourite hunting ground.

Police said Sinaga often went out after midnight, and in one of the closed-circuit television recordings, is seen returning to his flat just 60 seconds later with a young man who was later raped, the BBC reported.

Sinaga is believed to have used different ruses - offering a place to wait for friends, or to charge a mobile phone - to lure about 190 victims to his apartment. Most of them were in their late teens or early 20s, and had been out drinking before he approached them in the streets.

Many of Sinaga's victims recalled that he gave them a drink - which he once described in a WhatsApp group with friends as "secret poison" - when they went to his flat. He raped them after they passed out, filming the abuses on his two mobile phones.

One such clip showed a victim not stirring despite a mobile phone ringing at full volume in the background, The Guardian reported.

The prosecution said the men were drugged, likely with gamma-hydroxybutyric acid, better known as GHB or liquid ecstasy, or other substances with the same effect.

Sinaga was sentenced on Monday to 30 years' jail after he was found guilty of 159 offences, including 136 rapes.

Police believe Sinaga, who was arrested on June 2, 2017, would have carried on had one victim not woken up during an attack and called 999.

Following Sinaga's arrest, police discovered footage in two iPhones showing him raping scores of apparently sleeping young men.

When Greater Manchester police examined Sinaga's digital devices, they discovered 3.29TB of extremely graphic material - equivalent to 250 DVDs - depicting sexual assaults. In one case, the assault lasted for eight hours.

The victims did not know they had been raped until police tracked them down following Sinaga's arrest. They remembered Sinaga as a good Samaritan who had helped them out.

There were so many victims that his case needed four separate trials - with the first trial starting in June 2018 and the last one ending last month. None could be reported until restrictions imposed to avoid prejudicing juries were lifted on Monday.

The case has shocked many in Sinaga's home country of Indonesia, where homosexuality is still a taboo. Many condemned the abuses as evil and depraved.

The University of Indonesia, which confirmed that Sinaga is an alumnus, condemned his acts as "insolent, illegal and inhumane" and expressed its sympathy to the victims of his assaults.

Sinaga lived in Britain off money wired over by his father, an Indonesian tycoon who owns property businesses. Footage taken by the BBC showed his family's luxury house in Depok, West Java.

Born in Jambi, Sumatra, in February 1983 to a Catholic family, Sinaga is the eldest of four children. He attended a number of private schools and graduated with a degree in architecture from the University of Indonesia in 2006.

He went to Britain in 2007, when he was 24, to pursue his master's degree in planning and then sociology at The University of Manchester, graduating in 2011.

Sinaga had a lot of friends in Manchester, and boasted about his frequent "conquests" to his WhatsApp chat group. "He was very flamboyant, had highlighted hair and was very camp," one man who went out regularly with him was quoted as saying by The Guardian.

While in Britain, he worshipped at a liberal Anglican church close to his flat. Members of the church also provided the court with a reference.

"He did go to church and did some voluntary work, assisted with the service and with some classes too... He sees himself as openly gay. He liked the fact that the church accepted him as an openly gay man and also as being foreign as well," Detective Inspector Zed Ali, the senior investigator in the case, was quoted as saying by Manchester Evening News.

The Indonesian embassy in Britain revealed late on Monday that it had been following Sinaga's case for the past three years to ensure his rights were protected. Sinaga had legal counsel appointed, the embassy said, according to The Jakarta Post.

"The efforts were carried out to ensure Reynhard was afforded the full extent of his rights to protection and a fair trial in the UK justice system," the embassy said.