Sydney man jailed over child sex offences

Harrison Falkenmire responded to a 13-year-old girl's online ad seeking sex education by having sex with her, and humiliating and demeaning her, a court has heard.

Six years later, the girl, now a young woman, told the NSW District Court she is still learning to cope with the consequences.

"When I think of what happened to me, it makes me feel sick," she wrote in a victim impact statement read out earlier this month.

"I was a kid who needed someone to care about me and he took advantage of that in the worst possible way."

Falkenmire, 29, was on Wednesday sentenced to at least 20 months in jail after pleading guilty to acts of indecency with a person aged under 16, possessing child abuse material, procuring a child for unlawful sexual activity, and having intercourse with a person aged aged between 10 and 14.

According to court documents, he and the girl engaged in sexual activity in 2011 within a few months of him responding to her advertisement on social media site Teenspot.

Falkenmire told doctors later that he wanted to test out the alpha male ideal, but he knew his dominating conduct was not acceptable to his partner, Judge David Frearson said in his sentencing remarks.

Chat logs showed the girl was treated in a humiliating and demeaning manner, Judge Frearson said.

The court previously heard from Falkenmire's treating psychologist that he was on the autism spectrum, and it affected his understanding of the crime and his victim's age.

But Judge Frearson said evidence showed Falkenmire knew his actions were illegal.

"He clearly knew he wasn't supposed to be engaging in sex acts with a child, even as an experiment," he said.

The judge did appreciate that Falkenmire's decisions were clouded by his autism spectrum disorder, and that he failed to appreciate the consequences of his conduct.

He gave consideration to Falkenmire's condition in sentencing. Falkenmire will be eligible for parole as early as July 2018.