The Crown says Fawcett - then aged 21 - either took part in the killing, or was there as a party to the brutal murder.
Miss Manning's partially naked body was discovered floating in the Avon River the day after she was killed.
Today, the Crown said Fawcett was supposed to carry out the hit, but when the time came, he couldn't do it.
During a series of police interviews, he implicated himself in the killing, saying he'd been there while others carried out the vicious fatal assault, the court heard.
He told police during one interview that he had shut his eyes and hit her with a crudely-fashioned metal pole weapon.
Mobsters barked and said "Sieg heil" as they killed her, he claimed.
But Fawcett, who has been conducting his own defence with help from an amicus curiae, lawyer Craig Ruane, said during his closing address that he had lied throughout the police interviews.
"I stupidly implicated myself into a serious crime," he said.
"I lied. People lie for many things ... but I did not take part in this lady's death."
He highlighted evidence from the Crown that says Miss Manning was picked up from her spot on Manchester St at 10.43pm.
Police later established that it would have taken around six minutes to drive to the Mongrel Mob's gang-pad at Galbraith Avenue. Since the Crown says she was probably dumped in the river at around 10.59pm, it meant gangsters had just 10 minutes to rape and kill her.
"Impossible," Fawcett said.
"I was never at the gang pad. I didn't take part in this. It's all just a made up theory."
The trial has heard that semen found on Miss Manning's body belonged to an unknown person, known as 'male b'.
Fawcett denied knowing who that person was.
"I've described other patched members who seriously assaulted Miss Manning.
"I'm wanted by the Mongrel Mob. I'll never protect 'male b'. I've got nothing to gain from it."
After the closing addresses today, Justice David Gendall sent the jury home for a three-day weekend.
The judge will give his summing up on Monday before the jury begins its deliberations.