A clinical psychologist determined a 13-year-old boy was mentally capable to go on trial for murder because of his physical appearance.
The boy, who cannot be named for legal reasons, is one of eight charged over the death of Melbourne 16-year-old Declan Cutler.
The teen was stabbed to death in a Reservoir street on March 13 this year.
All of the accused are appearing in a children's court this week where a magistrate will determine whether there is enough evidence for the case to go to trial.
A clinical psychologist wrote a report for the court on whether the 13-year-old had the mental capacity to know what he allegedly did was wrong.
The psychologist told the court the boy was capable, despite never interviewing the teenager.
She told the court she watched hours of police tapes and body-worn footage of the boy in custody between the ages of 10 and 13.
The psychologist said he had physically matured in that time - he was taller, more slender and his facial features changed - which would correlate with cognitive development.
She told the court when a child was more cognitively mature, they would be less impulsive and more capable to use reason.
The woman also wrote in her report that the 13-year-old played a planning role in his previous offending and there was no evidence he was a follower.
When the 13-year-old's lawyer asked the psychologist if she was referring to an incident where the boy allegedly spat at a security officer, the woman said yes.
But when it was put to the psychologist that other reports determined the 13-year-old was easily led by others, she rejected the premise.
"I can accept there's other opinions," the woman told the court.
The magistrate said she would not rule on the question of whether the 13-year-old had sufficient knowledge for criminal intent.
She would instead only focus on whether there was enough evidence for all or some of the accused to stand trial.
A forensic pathologist also gave evidence in the children's court about the cause of Declan's death.
She said an autopsy revealed the 16-year-old had numerous injuries including four stab wounds to his chest and back.
A knife to the heart was the probable cause of death, although the pathologist could not say which of the four chest wounds led to the fatal injury.
After viewing CCTV footage of the incident, the woman said she also could not say who delivered the fatal blow.
The committal hearing will continue on Thursday.
