Detectives have arrested a man following an assault and stabbing on Friday evening which are believed to be linked.
In the first incident, it is alleged two male offenders assaulted a man in a chemist at a shopping centre on Cheltenham Road in Keysborough, on 13 June about 4.55pm.
The 70-year-old victim was allegedly assaulted by the pair when he intervened as they tried to leave the store, with suspected stolen items.
The Dandenong North man was taken to hospital with serious but non-life-threatening injuries.
In the second incident, a 16-year-old boy was waiting at a bus stop in Centre Dandenong Road in Dingley Village when he was approached by what is believed to be the same two offenders about 7.15pm.
The Dingley Village teenager was then allegedly stabbed in what appears to have been an unprovoked attack.
He was also allegedly assaulted as he tried to get away.
The boy was transported to hospital with serious injuries.
Local police, detectives and the Dog Squad quickly converged on the area and searched for the pair, who fled the scene.
Detectives attended an address Bonbeach this morning and arrested a 19-year-old man.
The Bonbeach man was taken to hospital with non-life-threatening injuries and is set to be interviewed at a later stage.
The second offender remains outstanding, and investigators will continue to make enquiries into his whereabouts.
Anyone with information, or anyone who may have witnessed the incidents or with dashcam footage is urged to call Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au
