Jackson Williams had been out clubbing and drinking when he attacked the 39-year-old from behind as she walked to work through the CBD early on October 28, 2018.

CCTV showed Williams grabbing the woman in a headlock and pulling her into Healeys Lane as she screamed and struggled.

He put his hand over her mouth and was on top of her before running away when an off-duty police officer intervened.

Williams was found not guilty in Victoria's County Court on Tuesday of assault with the intent to commit a sexual offence.

But the 21-year-old was convicted of an alternative charge of common assault.

He faced a judge-alone trial because of the suspension of juries during the COVID-19 pandemic.

Judge Mandy Fox said the attack was clearly intentional and violent.

But she found there wasn't enough evidence to prove beyond reasonable doubt Williams intended to sexually assault the woman.

He might have been trying to do this but also could have been trying to commit a robbery, Judge Fox added.

"It is important not to approach the question from the point of view of, 'well what else would he have been intending?'" she said, as this risked reversing the onus of proof.

"It seems that whatever intention he formed was formed within seconds, and I find it unlikely he had much of a plan."

Williams did not attempt to sexually touch or undress the woman or himself.

He went to police the next day after seeing CCTV of himself on the news.

He said he'd been drunk and didn't give evidence at his trial. It wasn't disputed he'd grabbed the nurse as she walked to her job at an inner-city hospital.

The woman told the court she'd been really frightened and scared, because Williams was really strong and she was too weak to fight him off.

She bit him in an attempt to free herself before a New Zealand police officer, who was in Melbourne on holidays, intervened.

Prosecutor Stephanie Clancy previously told the court it "strained credulity" to suggest the man was trying to do anything other than commit a sexual assault.

But Williams' lawyer, Rosalind Avis, said another motive such as theft couldn't be ruled out.

The man remains on bail and is due to return to court for a plea hearing on November 12.

Australian Associated Press