In the past, couple had fallen victim to home invaders, violent criminals who attacked these folk in their own home, a place where they should be safe, should be ... not were.
They were not safe, they were attacked and robbed and they took action in hopes of preventing that from happening again. Hope misplaced, proven so by a lack of change.
Watch through this video and see how well their precautions worked.
They placed one or more cameras, then their house was invaded again. The camera's caught images of their attackers, hopefully allowing the police to arrest them, but they did not stop the intruders, did not prevent them from assaulting and injuring them. I hope for their sake that they realized that as they lay in their hospital beds.
A gate might have stopped their attackers, the sight of a gun may have turned them away, such precautions might have safeguarded them from harm. The camera only served as an aid for punishing the criminals after the fact. Had those invaders opted to kill them, they would be just as dead.
"Never again" is an intention and a promise that needs to be enforced. If you desire to never again be subjected to violence, then it falls onto you to be able to enforce that desire in an effective manner.