In the opening day of a Calgary grandfather's trial in the 2015 death of his grandson, the courtroom heard a man had called Child Protective Services because he "thought something was wrong".

"I just wish I could have saved him," said Pablo Polomera, of five-year-old Eneas Emilio Perdomo, who went by ‘Emilio.’

Allan Perdomo Lopez, 59, is facing a manslaughter charge in the death of his grandson.

Polomera, a Crown witnesses, had a booth at a flea market where the Perdomo family frequented and testified the boy had a ‘patch on his head’, was ‘walking slowly’ and being ‘pushed along’ the last time he saw him shortly before he died.

In the Crown prosecutor’s opening statement, Vicki Faulkner said the boy had moved from Mexico and was living with his grandparents in Calgary when he was taken to hospital in medical distress in July of 2015.

"He was happy and healthy until he came to Canada for a better life," said Faulkner.

The boy arrived in Calgary in February, 2015 and months later, was brought to the South Calgary Urgent Care Centre with a traumatic brain injury. The Crown said that the boy had surgery at Alberta Children's Hospital but he succumbed to his injuries and died in hospital.

The prosecutor said an investigation began immediately into the boy’s death because the explanation about the boy’s fall down the stairs didn’t make sense.

Court heard that Emilio had bruises all over his body and that he had patterned scars on his back. An autopsy determined that the cause of death was blunt force trauma.

Carolina Perdomo, the boy’s grandmother, was also charged with manslaughter but the charge was stayed in February.

Emilio’s grandmother in Mexico testified through a video link. A pediatrician who examined Emilio when he first arrived in Calgary also took the stand.

Several witnesses are expected to testify including a former neighbour and a number of medical professionals.

The trial for Allan Perdomo is being heard by judge alone and is scheduled to last four weeks.