A Perth man who chased a teenage dirt bike rider in a case of "misguided vigilantism", causing the 15-year-old's death in a crash, has been warned to expect an immediate jail term.
Jude Nathan Francis, 26, was 25km/h over the speed limit when he tailed Mitchell Chase in Aubin Grove in December 2016, suspecting the boy was riding a motorcycle that had been stolen from him.
The pursuit caused the teen to look over his shoulder in fear at the offender's car, go through a give way sign and slam into another vehicle.
Mitchell was thrown from the bike and died in hospital the next day.
After Francis observed the motorcycle wasn't his, he drove home and didn't report the incident to police, but officers came knocking days later.
He pleaded guilty to three offences including manslaughter and is due to be sentenced in the Supreme Court of WA on Wednesday.
During submissions on Tuesday, the prosecutor described the offending as "misguided vigilantism".
Parallels were drawn between the case and the death of Kalgoorlie teenager Elijah Doughty, who in August 2016 was run down and killed by a man who was trying to reclaim his stolen dirt bike.
The court heard Francis was also trying to retrieve his dirt bike and had been disqualified from driving at the time of the crash.
Justice Bruno Fiannaca said Francis would be sentenced to an immediate term behind bars.
He was remanded in custody overnight after previously being released on bail.