Dumas found her seven-year-old son Nathan Dumas, who is Kuijers stepson, critically injured.
The cause of Nathans death has not been released.
Authorities said they will be issuing a Canada-wide warrant for a St. Catharines man in connection with a first-degree murder and an attempted murder on Friday.
His mother, Whitney Dumas, wrote a note on Facebook Sunday: "Your kind words and well wishes and downpour of donations have been truly overwhelming. Each one we have to work through, but we have nothing concrete right now", Gavin said. We have three kids, said Dumas, who had been in a relationship with the man for almost six years.
"We would certainly ask the public to take a look at that photo, and to familiarize themselves with it", Gavin said. Police said he was transferred to hospital in critical condition from his home on Queenston Street. "This has impacted the entire community", Gavin said during a press briefing at the NRP's St. Catharines office.
Dumas said she doesn't understand why anyone would hurt her son other than as a way to hurt her.
The search continues for a St. Catharines man accused of killing his stepson and attempting to murder a bank employee. He was rushed to hospital but died from his injuries early Saturday morning.
"A situation like this, it impacts the community, it impacts the family", he said.
Police described Kuijer as armed and unsafe.
The suspect van's licence number was BYTE392, police said. Police add that it wasn't a robbery, and that the victim had a "professional relationship" with him.
Initially treated at the St. Catharines site of the Niagara Health System, the woman was transported to a trauma centre outside of the Niagara region.
He then fled the scene in a grey 2009 Pontiac Montana van.
As of Monday, the boy's stepfather, 43-year-old Justin Kuijer, remained at large. They said if members of the public see him, they should not approach him and call 911 immediately.
Gavin said there is a floral sticker on the back of the van in memory of missing women in Canada related to Ashley Simpson, a St. Catharines woman and Dumas's friend who disappeared in British Columbia in 2016.
Kuijer is described as a white man, with a thin build, trimmed beard and longer dark hair.
"Where he may be going we just don't know", Gavin said Monday. He was wearing a black toque, brown leather coat, dark trousers, boots and an orange hoodie.