A search for an Ontario man accused of fatally injuring his stepson moments before attempting to kill a local bank employee stretched into its third day on Monday as police conceded the fugitive could be just about anywhere.

Niagara regional police said they've issued a Canada-wide warrant for the arrest of 43-year-old Justin Kuijer of St. Catharines, Ont.

The former owner of a roofing company is wanted on charges of second-degree murder in the death of seven-year-old Nathan Dumas, as well as the attempted murder of a woman working at a local RBC branch.

Const. Phil Gavin said Kuijer has been on the run in his ex-girlfriend's van ever since the two grisly scenes unfolded on Friday, adding that police have few leads as to his whereabouts.

"Where this occurred is less than a kilometre to the Queen Elizabeth (high)Way, and he's in a car, and it's three days later," Gavin told The Canadian Press in an interview. "The reality is he could be a lot of different places."

Gavin said police first learned of trouble around 10:15 a.m. on Friday when police were called to a home above a sandwich store owned by the victim's grandparents.

He said a family member found Nathan suffering from critical injuries and had him rushed to a hospital, where the boy died the next day.

At around the same time the Dumas family was making the discovery, police allege Kuijer walked into a nearby RBC branch and stabbed a woman working there. Gavin said Kuijer had a professional relationship with the woman and described the attack as targeted, but declined to provide further details.

The woman is now in hospital in stable condition, he added.

Police had originally indicated that they would be seeking a charge of first-degree murder in Nathan's death, but Gavin did not explain why the second-degree murder charge was listed on the warrant.

"At the 11th hour the decision was made that this was the most appropriate charge," he said.

Kuijer fled the scene in what police describe as a dark grey van with a distinctive pink floral missing person's decal on the back window.

The decal references Ashley Simpson, a Niagara-area woman who went missing nearly a year ago and was among the best friends of Nathan's mother. Gavin said it's possible the decal has been removed by now and urged the public to be on the lookout for a van with the Ontario license plate BYTE 392.

Kuijer was last seen wearing an orange hoodie under a brown leather coat, dark pants, a black toque, and boots, police said.

When reached by phone, Nathan's mother, Whitney Dumas, declined to offer comment. But a series of emotional Facebook posts suggests she and her two other children are struggling to come to terms with the loss.

"This is truly a tragic time for everyone involved. I understand that everyone has questions, it's human nature, so do I," Dumas wrote. "I kindly ask that everyone respect my family's privacy and space and allows my family this time to mourn the loss of my beautiful son."

Dumas thanked the Niagara community for an outpouring of support and a wave of financial generosity, and social media comments suggested those beyond the family circle felt moved by Nathan's death.

"My kids and I said a prayer tonight for you and your family," wrote one Facebook user. "You not only have a city, but a region...probably a nation at this point...supporting you."

An elementary school near the scene where Nathan died flew a flag at half-mast on Monday afternoon, and crowdsourcing efforts to raise money for the family generated considerable response.

Friends of the boy's family started a GoFundMe campaign that had netted more than $12,500 by Monday afternoon, eclipsing the original target of $10,000.

The page suggests Nathan died just a week shy of his eighth birthday.

"Nathan's precious life was abruptly cut short at the hand of someone else," the page reads. "Nathan was an energetic, loving and caring little boy who will never have his first girlfriend, graduate school or get married and have children. Nathan would have made a big difference in this cruel world."

Little is known about Kuijer, who listed himself as the owner and operator of Niagara Elite Roofing. Calls made to company phone numbers were not answered.

Michelle McQuigge, The Canadian Press