Jeffery Longman says that his grandson, Nikosis Cantre, died of a blunt force trauma to the head.

The six-week-old boy was rushed to hospital Sunday morning. A 16-year-old girl is in custody, charged with second degree murder.

Police were called to a house in Saskatoon, on Waterloo Crescent at 7 a.m. CST on Sunday with reports of an injured toddler. The teen was charged with murder later that day.

Longman said Nikosis's mother, Alyssa Bird, had gone out to buy breakfast that morning. She left the baby in the care of her older sister, Larissa.

The teen, who the family had only met the day before, was also in the house.

"When she got back, she noticed that the girl was coming out of the infant's room. That's when she noticed, like why is she coming out of my baby's room, I'm gonna go check," Longman said.

Flowers and stuffed animals were placed around a poster made in memory of baby boy Nikosis Cantre, who died July 3. A 16-year-old girl is accused of second-degree murder. (Chanss Lagaden/CBC)

The baby was unresponsive and barely breathing, he said.

They called 9-1-1.

Police have not said how the baby died.

Nikosis Cantre will be buried this weekend at Gordon's First Nation.