SARNIA, ONT. As London copes with the deadly collapse of a four-storey building under construction, the City of Sarnia is remembering another deadly cave-in. Twenty years ago today, Dec. 14, 2000, a portion of the roof above Lambton Mall collapsed, killing one store employee, 46-year-old Susan Foster. A heavy snowfall had built up on the roof leading to the tragedy. Sarnia Mayor Mike Bradley, who broke up with emotion twice during an interview with CTV News, says the incident remains fresh in the community’s mind. “It was very traumatic. I knew the family, and I knew the woman killed.” Bradley, who was in his office that morning, rushed to the scene just after 8:30 a.m.