Glen Luther, a professor at the U of S College of Law, said the government of then-Prime Minister Stephen Harper streamlined the Criminal Code's provisions on self-defence in 2012.
"I think the old law was exceedingly confusing. And so I think everyone that knew about this area of the law, and certainly academics like myself were pleased to see the change," he said.
The changes pared seven complicated sections of the Criminal Code down to two relatively simple ones: one covering self-defence and another covering defence of property, according to Luther.
A determination of self-defence is now based on three factors. Under section 34 of the Criminal Code of Canada: A defendant has to be reacting to force or the threat of force, they have to have acted to defend themselves or someone else and they have to have acted reasonably in the circumstances.
Luther said this is a contrast to how things were under the former laws, where prosecutors could have a difficult time gauging their odds of getting a conviction.
"Under the old law, we'd be looking at four or five possible arguments the defence would make. It was exceedingly complicated to predict what the jury might do," he said.
Luther said Canadian prosecutors generally use a two-stage test in deciding whether to pursue charges: whether they think they'll get a conviction and whether a proseccution is in the public interest.
While police haven't released much information in the case of the death on Preston Avenue, Luther said it's clear prosecutors didn't think there was enough there to convict.
"They're not saying for sure that they agree that she was (acting) in self-defence, but that that's the likely outcome of a trial, is that a jury would find that she acted in self-defence under the terms of the Criminal Code," he said.
Luther suggested courts have tended to allow more leeway to people protecting their homes.
"The Common Law has always held homes to be a place of special protection. The old language of 'a man's home is his castle' still is part of the legal tradition in this country," he said.
But Luther warned there still aren't clear guidelines on exactly what actions people can take to defend themselves.
"Certainly, one needs to be concerned of not using too much force. The problem with the law is that it's so general in this language of 'reasonable in the circumstances,' it's hard to classify that exactly," he said.