Queensland Police have taken two more people into custody as they search for the killer of a grandmother fatally stabbed outside a Brisbane shopping centre.

Police confirmed the apprehensions on Monday afternoon, although they refused to release more details.

“I will confirm that they are two juvenile males located walking away from her car. They were found through our inquiries today,” Detective acting Superintendent Heath McQueen said.

It came as a 15-year-old boy was due to face court after 70-year-old grandmother Vyleen White was fatally stabbed in front of her six-year-old granddaughter outside a shopping centre at Redbank Plains, west of Brisbane on Saturday.

She died at the scene a short time later.

The girl was unharmed.

The 15-year-old handed himself into Ipswich Police Station on Sunday night. He has been charged with unlawful use of a motor vehicle.

Detectives earlier released CCTV footage depicting four youths in an allegedly stolen Hyundai Getz.

The search for the last youth continues, although police say they know who he is.

“Sadly, the motive was to steal a Hyundai Getz. I stand before you today to talk about a murder of a grandmother in front of her granddaughter and the result was a stolen Hyundai Getz,” McQueen said.

“It is a callous, cowardly, violent crime … She was a 70-year-old grandmother, she was a loving family woman … This is senseless violence … She was taking her granddaughter to the shops.”

Floral tributes for White were left at the entrance of the Redbank Plains shopping centre on Monday as family and friends mourned her loss.

A GoFundMe page organised by family friends has already raised more than $7600.

“They have lost a mother, grandmother, a wife and loved family member of their family,” the fundraiser page said.

“They are all so overwhelmed and so warm hearted by the community at such a difficult time.”

Fundraiser Katherine Lameree said the page hoped to raise money for the funeral and other expenses but also to let the community know about White’s legacy.

“She was such a selfless woman – with so much care for her family and absolutely any one she came into contact with,” the page said.

“She would hold prayers for anyone who needed them.

“This is what they want her to be remembered by and not defined by the act of someone else.”

Police will also boost patrols in the area Redbank area following Saturday’s attack. Ipswich district officer Superintendent Kylie Rigg said a mobile base would remain at the shopping centre for 12 hours a day for the next fortnight.

“We will also have police deployed around the neighbouring suburbs, and we have resources available to do that,” she said.

“What has occurred here over the weekend was a callous, unprovoked, and violent attack on an innocent member of our community. It shouldn’t happen here, it should certainly not happen anywhere else in the state.”

Ipswich Mayor Theresa Harding said on Monday the attack was not a typical crime for the area.

“It’s really shocking for us as a community,” she told Seven’s Sunrise program.

Some Redbank Plains residents want more police presence at the shopping centre following the attack.

“The community want a permanent police beat at the Redbank Plains town square,” Harding said.

Queensland Premier Steven Miles has described the attack as “an abhorrent crime, a terribly violent crime, a crime committed … in front of a very young relative of the victim”.

-with AAP