Can a security guard use weapons to kill for self-protection?

What I understand from this Brother Eli's video:
https://3speak.co/watch?v=fatimajunio/kiliyvas

The main duty of a security personnel is to protect the lives of people. You have a weapon to do this work against criminals with weapons too. Since you're protecting other people's lives, it is not a sin for you to protect your own life when in danger.

The act of self-defence is permitted in the Bible. The book of Numbers 35:10-15 is where God commanded the Israelites to provide cities of refuge where anyone that kills another accidentally may run to for safety.

This means that it's not a sin in the sight of God if you kill someone while protecting lives and property.

However, it is advisable for security officers to be sharp shooters so as to aim well, and avoid heads and chests but, aim at the legs and hands. This is just to demobilise the criminal and hand him over to the law to have his fate decided by the law.