If the thug is threatening other peoples lives or safety than the security guard should do what is necessary to save those innocent people . If that means shooting a criminal so be it. Its more important that innocent civilians and cops are safe than some violent criminal .If you dont want to get shot dont commit crimes.
Without the ability to kill to prevent a madman from massacring others, the security guard is rendered as useless as the security monitor on that commercial. With only the clause of self-defence, he can only kill to protect his life, not those around him - those he was hired to protect. While this is not a home, I would think the same thing would apply here.
(BTW - he is neuter, women can be security guards too :)