Police charge trio with Darwin man's murder in alleged 'vicious attack'

Martin Wiberg died in hospital after an alleged "vicious attack" at the Casuarina bus stop in March. (Supplied)

Northern Territory Police have upgraded the charges against three men who allegedly beat 48-year-old Darwin man Martin Wiberg to death in a "vicious attack" at the Casuarina bus stop earlier this year to murder.

Police initially arrested four men aged between 19 and 30 after they allegedly knocked Mr Wiberg to the ground and stomped on his head on March 12, rendering him unconscious.

Paramedics rushed Mr Wiberg to hospital in a critical condition, where he allegedly died from his injuries two months later.

Martin Wiberg has been remembered as a "beautiful, kind, caring man" with a "heart of gold". (Supplied)

In a statement released today, an NT Police spokesperson said three of the four men, who were originally charged with aggravated assault, had had their charges upgraded.

"The Major Crime Squad has continued to investigate the incident and subsequently submitted a brief to the Director of Public Prosecutions (DPP) seeking to upgrade the charges from aggravated assault to murder," they said.

NT Police have upgraded the charges against three men over Mr Wiberg's death at the Casuarina bus stop. (ABC News: Tristan Hooft)

Mr Wiberg's loved ones have remembered the animal lover and karaoke enthusiast as a "beautiful, kind, caring man" with a "heart of gold".

Friends of Martin Wiberg are remembering him as a "very gentle soul".

Detective Senior Sergeant Paul Morrissey said today the 48-year-old's family remained "at the forefront of investigators' minds".

"Our thoughts remain with the family and loved ones of this man as they continue to endure an unimaginable loss," he said.

Two of the men, aged 26 and 31, are due to face the Darwin Local Court tomorrow, while the remaining 19-year-old is due to appear on August 12.