Police have concluded that the December death of a six-week-old Hamilton baby is not a criminal matter.

"It was a complicated case," said regional coroner Dr. Jack Stanborough. "Probably one of the most challenging I've faced in years."

Police say the infant was brought into Hamilton General Hospital on Dec. 23 showing signs of distress and died the next morning.

Originally, police said an autopsy suggested the baby boy did not die a natural death. However, after what Stanborough called an "extremely thorough investigation," that was deemed to be false.

"There was an element that was suspicious," Stanborough said, adding that police are required to treat any death of a child under five as suspicious.

"But the responsibility of this death could not and should not be laid on anyone's head."