The Crown says Fawcett - then aged 20 - either took part in the killing, or was there as a party to her murder.
Miss Manning's mutilated and partially-naked body was discovered floating in the Avon River the day after she was killed.
Blood, urine and other samples were taken from her body and sent for analysis by ESR forensic scientist Helen Poulsen.
High levels of methadone were found in her system, which Dr Poulsen said today indicated Miss Manning had a high tolerance for the drug or she was a regular user.
There were also trace levels of morphine, diazepam, possibly temazepam, and THC, the active ingredient in cannabis.
Morphine doesn't stay in the body for more than a few days, Dr Poulsen said, while the THC findings meant that Miss Manning must have smoked cannabis "fairly shortly" before her death.
There was no alcohol found in her blood or urine, the court was told, and there was no evidence of methamphetamine in her system.
Dr Poulsen couldn't say how affected by drugs Miss Manning was at the time she died.
Miss Manning had been working on her usual patch on the corner of Peterborough and Manchester streets on the night she was killed.
In his first police interviews, Fawcett described how Miss Manning was taken to the gang pad at Galbraith Avenue, Avonside, where she was raped, bashed and stabbed.
Fawcett initially told police that Mongrel Mob gangsters barked like dogs and gave Nazi salutes as they carried out the fatal assault. She was then dumped in the river 200 metres away.
Fawcett later backtracked from his earlier version of events, saying he wasn't present during the attack.
Telecommunication data experts have also been giving evidence today.
The jury heard that Miss Manning made a final call from her cellphone at 10.42pm on the night she was killed, and sent a last text message at 10.43pm.
The trial, before Justice David Gendall, continues.
