If it turns out to be a felon in possession of a stolen firearm.

Armed robberies need additional mandatory jail time.

Felony larceny of a firearm should also carry some hard time.
No plea bargains with these crooks.

The "suspect" will try again in the future.

Kudos to the store clerk, but people should understand that it can happen in a parking lot, restaurant, any public place that firearms are not allowed.