Three people have been detained, while a fourth is yet to be interviewed by police.

Aiden Becker was allegedly stabbed while defending a teenager.

A young off‑duty security guard has been identified as the man allegedly killed while trying to protect a teenage boy during a violent armed robbery at a train station.

Aidan Becker, 22, died at Mernda station in Melbourne’s outer north after he stepped in to help a 14‑year‑old boy who was being assaulted about 5.50pm on Friday.

Police say Becker walked the teen away from the platform, but the group allegedly followed — before turning on him.

“Unfortunately, those four offenders followed both of them and then, in what could only be described as a savage attack, assaulted the 22-year-old male physically, both fists, kicking, and they used edged weapons,” Homicide Squad Detective Acting Inspector Nigel L’Estrange said on Saturday.

He was punched, kicked and attacked with an edged weapon in a brutal assault that left bystanders rushing to perform first aid.

Paramedics arrived moments later, but sadly, Becker died at the scene.

Four males — a 16‑year‑old, an 18‑year‑old and two 17‑year‑olds — were arrested shortly after.

“This is just a tragic situation where our victim here is just a good Samaritan who was trying to do the right thing,” L’Estrange said.

“He’s intervened, tried to protect this 14-year-old schoolboy, hasn’t been aggressive at all, tried to remove him from the scene, and as a result of his interaction, he’s now lost his life.”

Homicide Squad detectives have now charged a 17‑year‑old from Greater Geelong and a 16‑year‑old from the Whittlesea area with murder and armed robbery.

Both will face a children’s court at a later date.

An 18‑year‑old Mill Park man has also been charged with murder and armed robbery and was due to appear in the Melbourne Magistrates’ Court on Sunday.

A fourth teen, a 17‑year‑old from the City of Yarra, remains under police guard in hospital and is yet to be interviewed.

Major Crime detectives continue to investigate the circumstances surrounding the fatal attack.

SOURCE: https://7news.com.au/news/offduty-security-guard-aidan-becker-killed-after-stepping-in-to-protect-teen-at-mernda-station-melbourne-c-21874372