Supreme Court Justice Christopher Beale on Friday said Fatah Issa had been suffering from severe post traumatic stress disorder because of his childhood experiences in war-torn Somalia when he attacked and killed Shaun Wright.

Issa, 27, was found unfit to plead to the murder charge in September last year because of mental impairment but after spending six months in the maximum security Thomas Embling psychiatric hospital, doctors decided he was well enough to plead to the charge.

Issa pleaded guilty to murdering Mr Wright and was jailed for 18 years with a non-parole period of 14 years.

Justice Beale said he had taken into account Issa's upbringing in Somalia and accepted his PTSD had contributed to his offending which reduced his moral culpability.

Issa was three when his family home was destroyed and he and three of his 11 siblings were taken hostage by militia. Two of his siblings were killed and he was held captive for 18 months before being returned to his family.

Issa's family managed to flee Somalia and spent time in a Kenyan refugee camp before emigrating to Australia on humanitarian visas.

Justice Beale said there was no doubt Issa's horrific childhood had contributed to his long-standing alcohol and drug abuse problems.

If Issa hears the sound of a door banging it reminds him of gunshots being fired in Somalia and he suffers from constant nightmares, the court heard.

Crown prosecutor Mark Rochford, QC, had told the court Mr Wright, 21, was killed during a night out celebrating a friend's birthday when he picked up a piece of wood and inexplicably threw it at a parked car on March 17 last year.

Three young African women in the car at the time got out and remonstrated with Mr Wright and his two friends before they ran off.

The women and another man then drove around Fitzroy looking for Mr Wright before they found him and chased him down a laneway.

During the chase, one of the women tripped and Issa, who did not know any of the people involved, asked if she was all right. The woman ignored Issa and continued to chase Mr Wright.

After the group of three women and their male friend cornered Mr Wright in Johnston Street, police claimed Issa suddenly appeared and struck Mr Wright several times with a broken beer bottle causing his death.

Issa had never met Mr Wright before the attack.

Issa later told claimed he was drunk and wrongly believed the African women were being chased and he wanted to help them.

Justice Beale said Mr Wright came from a close-knit family who had been devastated by his violent and premature death and their suffering was "intense and enduring".