Jaymes Todd says his rape and murder of aspiring Melbourne comedian Eurydice Dixon didn't go as he planned.
But two psychologists disagree about whether the killing was premeditated.
Todd set upon Ms Dixon, 22, as she walked barefoot through Carlton North's Princes Park on June 12 last year.
Then 19, Todd had stalked Ms Dixon for five kilometres from the city, where she had performed a comedy gig.
The Supreme Court of Victoria heard Todd had an obsession with porn depicting rape, strangulation and death and has since been diagnosed with sexual sadism disorder.
During a pre-sentence hearing on Friday, two experts agreed Todd's sexual sadism disorder motivated the attack, rather than his pre-diagnosed autism.
Forensic psychiatrist David Thomas said Todd hadn't planned to murder Ms Dixon and wasn't sure if he would "go the whole way" until the attack had started.
"'Going the whole way' is the fantasy to completion - the strangulation of the victim (and) the victim's death?" defence lawyer Tim Marsh asked.
"That's right," Dr Thomas replied.
But psychologist James Ogloff testified Todd intended to kill Ms Dixon as part of his fantasy.
"He knew he was causing incredible harm to this young woman and he did not stop. If anything he was aroused and excited," he said.
After the murder, Todd bought a pie and coffee, revisited the crime scene and searched the internet for rape porn and stories about Ms Dixon.
He handed himself in to police when friends saw him on the news, though he initially denied being Ms Dixon's killer.
Professor Ogloff said Todd's actions may be "profoundly disturbing", but it was not uncommon for people with autism.
"When I asked him to think about how he felt ending Ms Dixon's life, he could not articulate. He said, 'I didn't really have any feelings'," Prof Ogloff said.
The court heard Todd told his father he "felt like s***" and "hoped it would be better next time''.
When asked by Prof Ogloff to explain what he meant, Todd said he was "glad that he was caught".
"What frightened him is that he realised he had the capacity to carry out his fantasies," he said.
"He stated the offence didn't go as he had planned but he was unable to elaborate on that point."
Mr Marsh said his client lived in filthy public housing in Broadmeadows with his family at the time of the murder, but often preferred to sleep rough.
Vermin, food scraps and rubbish rendered most of the house uninhabitable. A hot plate in the bathroom next to a blocked toilet was the only place Todd could cook.
Mr Marsh said custody had proven to be a "better environment" for Todd, who kept his cell "as neat as a pin".
Justice Stephen Kaye earlier indicated he would consider imposing the maximum sentence - life without parole - if he found Todd's actions to be premeditated.
"In the 21st century that a young lady cannot, minding her own business doing no one any harm, cross a park without being sexually assaulted, raped and murdered in this way, is beyond belief and utterly despicable," he said.
The hearing will continue on Tuesday.