Moorabbin Crime Investigation Unit detectives have charged a further teen in relation to an armed robbery in Glen Huntly earlier this week.
It is alleged a 14-year-old boy was confronted by unknown offenders in a Volkswagen Tiguan about 3.35pm on Monday.
The teen was forced into the vehicle which has then driven along Neerim Road.
A short time later the victim has come out of the moving vehicle, in unknown circumstances, near the intersection of Grange Road and sustained significant injuries.
He was taken to hospital where he remains in a serious condition.
A 15-year-old Cranbourne boy was arrested in Mentone about 12.50pm on Saturday.
He has been charged with multiple counts of armed robbery, robbery, conduct endangering life, intentionally causing serious injury, theft of motor vehicle and theft.
He has been remanded to appear at a Children's Court at a later date.
The investigation remains ongoing.
Anyone who witnessed either incident, has CCTV or dashcam footage or any other information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au
