The argument for these cameras is that they save lives. The argument against them is that they destroy freedom.
That's why these cameras are so prevalent, the case for them is extremely obvious and easy to make (give police more tools to stop bad guys), while the case against them is a lot more subtle (human freedom, government abuse, expectations of privacy, risk of data breaches, etc).
Helping to solve a crime after the fact is certainly a thing, and that discussion has merit, but I think you’re taking creative license again with stopping a serial killer or spree killer “before they kill again.” That’s not really how murders play out, which is why there are special names for them.
It would be helpful for discourse, and for making your own argument, if the discussion was grounded in the reality of the sour world we live in now.