A “brazen” and “polished” sexual offender may have more victims who are yet to come forward, police believe.

Luiz Da Silva Neto, 35, was found guilty on Friday at Oxford Crown Court of drugging and sexually assaulting two men in November and December 2021.

The court heard that he drugged the men with an unknown substance that was likely to be GHB or GBL.

One of the victims was a married man who was on a night out with work colleagues in central London hotspot Raffles before he was assaulted.

A month later, Da Silva Neto targeted another man at the same location, drugging the victim and driving him back to his home where he assaulted him.

Police believe Da Silva Neto targeted heterosexual males because he thought they would be less likely to report him.

Thames Valley Police have urged anybody who thinks they may be a victim of sexual assault by Da Silva Neto, or by anybody, to come forward.

Senior investigating officer Inspector James Holden-White said: “When we look at the method of offending in this case, the ‘MO’ as we would call it, it seems very brazen, it seems very polished and quite accomplished, he knows what he is doing.”

He added: “We are continuing to investigate his activities, I cannot go into any of that, but what I will say is that if you think you are a victim of Luiz Da Silva Neto, or if you think you are a victim of similar offending by somebody else, please come forward, we will listen to you.”

The police detailed how Da Silva Neto visited several pub toilets and approached men to test their sobriety in order to identify victims before drugging them.

They said the case had similarities to the crimes committed by Reynhard Sinaga, the UK’s most prolific rapist, in Manchester.

Sinaga was jailed in January 2020 for drugging and raping more than 40 men, with his trial hearing that he targeted people by posing as a Good Samaritan before lacing his victims’ drinks with drugs such as GBH to render them unconscious.

It is believed he has more victims yet to be formally identified, as Greater Manchester Police received more than 155 reports following a public appeal after his conviction.

Mr Holden-White said: “I’m more concerned that this could be similar to the Reynhard Sinaga case in Manchester, which was also widely reported on, where a man did something very, very similar.

“He (Sinaga) is going into the night-time economy, he is targeting people who are already vulnerable and drunk, he is being a Good Samaritan, and offering to get them some food or call them a taxi or get them a drink.

“Sinaga then got them up into his flat which was very accessible to where he was and was then able to administer a substance and go on to sexually offend against them.”

Mr Holden-White has urged people in nightclubs and bars to remain vigilant, stay close to friends, and use night-time services such as social workers and police officers if they feel in danger.

He said: “I cannot stress how unusual and rare these kinds of offences are, I really do not want to cause any alarm whatsoever.”