An internet user who solicited girls for sexual activity in a cemetery wrote, "I am going to turn Sydney into a big underage gang bang", a judge has been told.

Daniel William Peckham also wrote, "I'll keep luring young girls into Satan's loving embrace of carnal delights".

The now 24-year-old penned the words in jail while on remand for 10 offences including sexually assaulting a 15-year-old girl in Sydney's Rookwood cemetery in April 2007.

During a sentencing hearing in the NSW District Court on Thursday, psychiatrist Dr Michael Diamond said Peckham's determination to obtain access to young girls was "the core of his existence".

He has pleaded guilty to the sexual assault, and to three counts each of using a carriage service to procure underage girls for sexual activity and to transmit child pornography.

Peckham has also admitted using a carriage service to menace one victim and two counts of attempting to pervert the course of justice.

According to the statement of facts tendered to Judge Peter Berman, Peckham set up a website, Rookwood Gothic Society, to solicit minors for sexual activity.

The site stated: "If you hang-ups about getting naked, then you are not welcome, and if you are not willing to let me have sex with you, then you are not welcome".

In response to his grooming, a 13-year-old girl sent him her topless photo, talked online with him about sex and kissed him during the four hours she spent with him at the cemetery.

He met three of the underage girls at the cemetery, including a 15-year-old he digitally penetrated.

Giving evidence for the Commonwealth Director of Public Prosecutions (DPP), Dr Diamond concluded Peckham "would be at risk of repeating his conduct".

His "procurement or orchestration" of opportunities to make contact with young girls was "the total preoccupation of his life at that time", the psychiatrist said.

Dr Diamond said he had read a "voluminous" journal kept by Peckham, as well as his other writings and letters he sent while on remand in jail.

He agreed that Peckham had "grossly deficient social skills" and a propensity for self harm.

Psychologist Dr Emma Collins, called by the defence, concluded he was only a moderate risk of repeating his conduct if he undertook sex-offending treatment.

Bruce Levet, for the DPP, read extracts from Peckham's journal and letters, including: "I got into the newspapers apparently.

"It's times like this I wish I'd done more so I could get busted for it and become even more infamous".

Ms Collins said Peckham wrote exactly how he felt, in a "very immature manner, quite adolescent".

She agreed his jail letters had an overwhelming theme about wanting to have sex with young girls, but stressed he had not yet received appropriate treatment for his offending.

In one letter he said: "I like schoolgirls, they excite me sexual" and in another: "I need 10 schoolgirls lined up in a row".

The hearing continues on Friday and the judge is expected to sentence him on December 4.