Joshua Robinson met two Singaporean girls online, court documents showed, and pressured them into having sex with him.
"There is no doubt in my mind that in doing what he did, the accused was a sexual predator," district judge Crystal Ong said in handing down the sentence.
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"The law must come down hard on such individuals so as to specifically deter them from re-offending and also to deter others from committing such acts against vulnerable young persons."
Both victims were only 15 years old at the time of the offences, which occurred between 2013 and 2015. The age of consent in Singapore is 16.
In both cases, Robinson filmed himself performing sex acts on the girls before having unprotected sexual intercourse, the court documents said.
One of the victims had a "mental breakdown" shortly after their encounter in June 2015 -- three months after she first started chatting with Robinson -- and told her parents, who made a police report.
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Robinson pleaded guilty last month.
Detectives who raided Robinson's Singapore apartment found close to 6,000 obscene films in his possession. More than 300 of the films featured children.
Robinson is also accused of showing an obscene video to a six-year-old child whose father attended his gym. The girl later told her mother about the incident and a separate police report was filed.
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