Based on what you've commented on here, you're pretty dense and need to actually look up the Charter of Rights and think about how else the police could possibly legally gather information.Police say the two dead men were the intended target. The other injured parties are just collateral damage. Police asking for help from the public. Query: Why should the public help, isn't that the police's job?
Bothering innocent people? How would you like that excuse from the police if you were the victim of a serious crime?
Imagine the police coming to you and saying they didn't go out to try and contact people living in the area to see if they were recording the incidents on their phone or had security cameras for their place. Then they tell you that they didn't want to bother asking people who were witnesses that didn't stay around because they had to pick up their kid from daycare or get home before the last train?
I bet you'd be the first to sue the police for an improper investigation.