A police investigation into the attempted murder of a five-year-old Calgary boy has led to separate charges against his mother for the prior death of one of her sons.

On May 27, police began investigating how a five-year-old boy ended up in a hospital struggling to stand up and also suffering breathing problems. His injuries were consistent with some form of trauma and not an illness.

Five days later, the boy's mother was charged with attempted murder, choking with intent and failing to provide the necessities of life.

From that initial investigation, police took a closer look at the mother's life and have now laid a charge against her in relation to a different child who died nearly six years ago.

Sean Ronald Fewer was found in his crib not breathing on Dec. 27, 2004. At the time, his death at only 10.5 months was declared to be from natural causes and no criminal investigation was launched. But police now believe the boy was smothered.

"An extensive criminal investigation was launched into the woman's history and that of her children," Sgt. Rick Tuza of the Calgary Police Homicide Unit told reporters on Friday.

"Based on information gathered by the investigators, the 2004 death of the woman's son has been reclassified as a homicide."

Tuza said he doesn't believe police made mistakes in the initial investigation, and added there was no indication at the time that a crime had taken place.

Stacey Joy Boudreaux, 33, now faces a charge of second-degree murder in the 2004 death of her infant son.

Tuza said Bourdeaux has co-operated fully with police.

She made a brief court appearance in Calgary Friday, when she stood quietly while the judge put the matter over until Monday. Bourdeaux's lawyer, Rupert Joshi, declined to speak with reporters.

Tuza also told reporters that Bourdeaux's husband, Edward Ronald Fewer, died accidentally earlier this year when he was electrocuted while trying to retrieve something from a power line.

With files from The Canadian Press