Prince Albert police have launched a homicide investigation after three people — including a seven-year-old boy — were killed in the Saskatchewan city on Sunday.

"It's a tragedy that's unimaginable for the community, our staff and definitely the family of the loved ones here who are now deceased," said Prince Albert police Chief Jon Bergen, describing what happened as horrific and incomprehensible.

Officers were called to a home on the 300 Block of MacArthur Drive around 4 p.m. CST on Sunday. They found a man and a woman, both 56 years old, and the boy dead. They also found a five-year-old girl critically injured.

Police have not revealed the relationship of the victims, but CBC News has confirmed that the two adults were grandparents to the children.

'The most difficult news'

Heather-lynn Sumners, the mother of the children, said she was not ready to speak with CBC, but pointed to the online fundraiser started for her and her family. It said that on Sunday, "Heather received the most difficult news of her life."

Her seven-year-old son Bentlee was dead and her five-year-old daughter Kendrah seriously injured.

It said Bentlee was born prematurely in Kamloops, B.C., "at a whopping three lbs., and from the minute Bentlee was born he was determined, and he was brave."

On Sunday, seven-year-old Bentlee was killed. His family says that Bentlee was born prematurely at three lbs, 'and from the minute Bentlee was born he was determined, and he was brave.' (Submitted by Destiny Bradfield)

Her daughter Kendrah is in stable condition, but only after she was tended to by medical teams in Prince Albert, Saskatoon and now Edmonton.

"Kendrah had three surgeries, but like her brother is determined and she is brave."

Kendrah's family says the five-year-old is stable in Edmonton after going through three surgeries. (Submitted by Destiny Bradfield)

The family has asked for donations to help with travel and funeral expenses, as well as to help Sumner's youngest son.

No suspect in custody

Bergen said there is not a suspect in custody and no charges have been laid. Police did say the incident was not believed to be random and insist there is no longer a threat to community safety.

"We're able to understand enough that we're comfortable making that statement," Bergen said. The police chief would not say whether investigators even had a person of interest and asked for patience.

"There's going to be a lot of speculation and people are going to require answers," he said. "We need to make sure that what we are seeing is what is accurate to what has happened."

On Sunday, police officers were called to the 300 block of MacArthur Drive. They located three deceased victims, of those who was seven-years-old, and a girl in critical condition. (Chanss Lagaden/CBC)

Bergen said police plan to release more information in the coming days and noted officers are examining "a great deal of evidence."

"That has led us to information that we understand where we need to go next."

He noted the "horrific" nature of the crime and the evidence will likely take its toll on the police service members.

"We can't imagine what that felt like, for each person who entered the scene," he said, speaking directly to the condition of the children.

"Our staff definitely took a call that nobody should have to take and it will have its impact."

The investigation is underway and members of the criminal investigations division and the forensic identification team remain at the home.