Cyr was 18-months-old when she disappeared on Aug. 15, 1978.
Her mother, Liliane Cyr, had left the girl in the care of a new boyfriend while she went to work in Quebec’s North Shore region for a week.
When she returned, Liliane Cyr's boyfriend told her that Johanna had drowned in the tub, and he had taken care of burying the girl.
Montreal police arrested the man, a 32-year-old American, at that time. However, he was released because police had no evidence that he had done anything illegal.
Police interest renewed
Montreal police reopened the investigation in 2011 into Cyr's disappearance after a woman who lived in the neighbourhood reported she had seen the boyfriend leave the house one evening around midnight, carrying a box.
The empty lot has since been paved over and is now a parking lot for a community centre.
In September, police called on students from Montreal’s École Polytechnique for help.
Investigators compared aerial photographs of the area taken in 1971 with photos taken in 1979.
They scanned the parking lot using a high-tech device and said they found two anomalies underground.
Investigators have now set up blue tents over the areas where the asphalt on the parking lot was dug up today.
They’re continuing the excavation work, digging by hand.
Liliane Cyr was present during the excavation work, hoping to learn more about what happened to her daughter.
"We're not finished yet, so I'm not going to move from here until I've got the answer," said Cyr.
"Maybe we will not find anything. That will be like another knife in my heart," she said.