Calgary police have charged the grandfather and step-grandmother with manslaughter in the death of five-year-old Eneas Emilio Perdomo after a year-long "monstrous" investigation.

Allan Edgardo Perdomo Lopez and Carolina Del Carmen Perdomo were charged Friday after the investigation determined the death was a homicide late last month.

Carolina Del Carmen Perdomo and Allan Edgardo Perdomo Lopez were charged Friday with manslaughter in the death of their five-year-old grandson. (Mike Symington/CBC)

Emilio was brought to hospital on July 10, 2015, suffering from injuries his grandparents described at the time as the result of numerous accidents.

"Medical staff observed swelling and bruising all over his body, which was not consistent with the activities of a child his age," police said in a release.

On July 17, 2015, the child died.

He was born in Mexico City and came to Calgary without his mother a few months before he died. His mother still lives in Mexico City, police said.

Acting Staff Sgt. Michael Cavilla said at a news conference Friday night, the investigation took more than a year because the "medical evidence is monstrous."

Acting Staff Sgt. Michael Cavilla said the year-long investigation was 'monstrous.' (CBC)

"We have radiologists, emergency doctors, forensic pathologists, neuropathologists all weighing in on this," Cavilla explained.

Defence lawyers for the couple criticized police last week for issuing a press release with the pair's pictures hours after, lawyers say, the couple had agreed to return from Victoria for questioning.

The lawyers said their clients had been subjected to a trial by media. The couple turned themselves in last Friday, were questioned and released without charges.

They are scheduled to appear in a Calgary courtroom on Monday.