JMO here, it's a legal, ethical and moral delima. What is legal is not always practical or prudent. Just because you can do a thing does not mean you should.
If you want to be under paid, under appreciated and over scrutinized, please attend a police academy and hire on, we can use you. If you are a LTC you carry to defend yourself, your family, and innocent others in that order.
The laws vary by locale as to the permissible use of force (and especially deadly force) to defend property and prevent the escape of a felon. Unless you are a licenced security guard it is not your buisness to use deadly force to safeguard other people's property.
A legally safe thing to say is that if you or an immediate family member is not threatened with potentially deadly harm, you should not indicate in any way that you are armed, but rather observe, and give a full account to authorities.
I say legally safe, not safe, because in the OPs senario, the schelm is committing multiple felonies, armed robbery, assault with a deadly weapon, armed criminal action, etc. He is likely a felon in possession of a firearm a federal felony. You are a witness to these crimes. Depending upon the sociopath's experience, and degree of cognitive function, he may decide killing potential witnesses is advantageous.
It is an incredibly subjective answer but if I believed the miscreant was going to grab the cash and run I would observe and report. If I could I would seek distance and cover.
I WOULD PROTECT MY FAMILY DESPITE ANY COST.
I WOULD NOT BE HOLDING A FIREARM WHEN POLICE ARRIVE.
I WOULD IMMEDIATELY FULLY COMPLY WITH ALL POLICE ORDERS.
OTOH, if I could clearly articulate a reasonable belief that the schelm was prepared to commit murder. I would place a round in the inverted triangle of eye-eye-mouth. Police officers have to give verbal warnings, if you can articulate an immediate mortal threat doing so is suicidal.
Remember this is just an opinion, and is worth what you paid for it.
PS: NEVER DRAW A WEAPON YOU ARE NOT PHYSICALLY AND ETHICALLY PREPARED TO FIRE, KNOWING THAT IF YOUR AIM IS TRUE YOU WILL TERMINATE A HUMAN LIFE. Know your actions will be scrutinized and you and your family will bear the consequences of your action or inaction.
It is certainly easier to let others make these decisions, this is a stage of life known as childhood. Once you get big-boy-pants you are responsible for yourself and your loved ones.