An L-plater who was high on cannabis ran a red light during a high-speed police chase and crashed into a bus, killing the 16-year-old passenger, a Perth court heard.
After the crash, a paramedic asked driver Steve Mason Mourish if anything hurt and the 19-year-old replied: "My heart hurts. I'm sorry I killed my brother", referring to his friend Jack Meier who died later in hospital.
Mourish, then 18-years-old, reached speeds of 155km/h in a 70km/h zone while driving drug affected in a stolen car before smashing into Shawn Jessep's bus.
Meier, 16, died after suffering multiple injuries to his head, chest and abdomen while Jessep, 46, was trapped in his vehicle and broke three rips and fractured his spine.
Mourish's lawyer, Simon Freitag, told the WA Supreme Court his client accepted responsibility for the harm he caused and was both appalled and distressed by what had happened.
At the scene, Mourish allegedly said sorry repeatedly and one officer replied: "That's what happens when you steal a car."
Mourish has pleaded guilty to several offences, including unlawful killing, aggravated dangerous driving causing bodily harm and stealing.
His lawyer said Mourish had a disadvantaged childhood and his life was "desperate and sad" even before the fatal crash.
Mr Freitag also claimed Mourish suffered from foetal alcohol spectrum disorder (FASD) but there had been no confirmed diagnosis.
Justice Bruno Fiannaca ordered neuropsychological assessment and an assessment by a paediatric specialist to determine whether Mourish suffers from FASD, which may affect his sentencing.