Three people have had their charges upgraded to murder following the death of a man who was allegedly assaulted at a Toowoomba taxi rank last week.

Robert Brown, 75, succumbed to his injuries in hospital on Monday, days after he was pushed to the ground and had his backpack stolen while he was waiting at the rank in the city's CBD.

Isaac Zane Cubby, 18, from Wilsonton, a 17-year-old Dalby boy and a 17-year-old Harlaxton boy, who both cannot be named for legal reasons, were all initially charged with grievous bodily harm over the incident.

The trio has now had their charges upgraded to murder.

Mr Cubby was remanded in custody and will re-appear in Toowoomba Magistrates Court on March 28.

The 17-year-olds also remain in custody and will appear in the Children's Court at a later date.

The teenagers were initially charged with several offences including grievous bodily harm after allegedly leading police on a chase in a stolen car after the alleged assault on Mr Brown.

Another 16-year-old boy in their company was later charged with unlawful use of a motor vehicle and has appeared before the Children's Court.

Investigations are still ongoing and witnesses or those with dashcam footage are urged to contact police. 

Mr Brown was remembered by the Toowoomba community as keen photographer with an infectious smile. 

A community forum was held in Toowoomba in the wake of Mr Brown's death amid increasing concerns about youth crime.