The Niagara Regional Police Service say a 43-year-old man is wanted for first-degree murder in the death of his stepson.

The man also is wanted in connection with a stabbing at a St Catharines, Ont., bank earlier this week that left an employee in serious condition.

Nathan Dumas, 7, died Saturday after being discovered in medical distress in St. Catharines on Friday. Police say he was transferred to hospital in critical condition on Friday from his home on Queenston Street.

His exact cause of death is not being released at this time.

Police are looking for Justin Kuijer, of St. Catharines, and describe him as armed and dangerous. Police plan to issue a Canada-wide warrant for Kuijer on Monday.

"We do believe the victims were targeted," Const. Phil Gavin of NRPS told reporters.

Bank stabbing, boy's death connected

Police didn't disclose the connection between the attack on the woman and the death of the boy.

The condition of the woman attacked has been upgraded to stable from serious condition. Police said the woman and Kuijer are "known to each other professionally."

Gavin wouldn't confirm what the professional relationship was.

Justin Kuijer is shown in a Niagara Regional Police Service handout photo. Niagara police are on the hunt for Kuijer, a 43-year-old Ontario man wanted in connection with a stabbing at a bank and his stepson's death. (Handout/Niagara Regional Police Service)

On Friday morning, police said a man stabbed the woman in an RBC branch on Martindale Road in St. Catharines.

Police originally reported the stabbing as a violent bank robbery at an RBC branch, but Gavin clarified on Sunday that it was not a robbery or a domestic dispute.

Police said the man fled in a grey 2009 Pontiac Montana van, license plate BYTE392. The van also had a pink-and-white decal in the back window for missing woman Ashley Simpson.

Kuijer is described as a white male with a tall, thin build, a beard and longer dark hair. He wore a black tuque and coat, boots and possibly an orange sweater.

<a href="https://twitter.com/hashtag/RBCInc?src=hash">#RBCInc</a> 13. Further information just in. The vehicle involved is dark grey in colour. Please see photo. If you see call 911 <a href="https://t.co/AuxcMymDTB">pic.twitter.com/AuxcMymDTB</a> —@PCPhilGavin

<a href="https://twitter.com/hashtag/RBCInc?src=hash">#RBCInc</a> 11. The suspect has been IDd as Justin Kuijer 43 yrs. from STC <a href="https://twitter.com/hashtag/NRPSWanted?src=hash">#NRPSWanted</a> Attempted Murder. Considered armed and dangerous. <a href="https://t.co/dZWDRCWMxR">pic.twitter.com/dZWDRCWMxR</a> —@PCPhilGavin

Police are treating the attack at the bank as an attempted murder.

Initially treated at the St. Catharines site of the Niagara Health System, the woman has been transported to a trauma centre outside of the Niagara region.

Anyone who sees the van, or has information, should call (905) 688-4111.

"Should a member of the public observe or know the location of Justin Kuijer, do not approach him," police said.