Robert William Boettger, 28, has now been charged with second degree murder in connection with the death of four-year-old Rayna Gagne.
He had been charged with aggravated assault in the case and made a court appearance on Monday.
Waterloo Regional police detectives are apparently continuing their investigation, and the suspect is expected to appear in court on Wednesday to face the upgraded charges.
Gagne died in hospital two days after emergency services were called to her home in Cambridge for an unconscious child.
A post mortem examination found head trauma was a contributing factor in her death but further testing has been scheduled.
Anyone with information is asked to contact police at 519-650-8500 Ext. 8669 or Crime Stoppers at 1-800-222-8477.
