A few examples from a quick search on FR:
Employee killed trying to prevent liquor store robbery in West Covina
https://freerepublic.com/focus/f-news/4188445/posts
California Home Depot employee shot, killed trying to stop suspected shoplifter
https://freerepublic.com/focus/f-news/4146828/posts
Employee killed while confronting shoplifter taking ammunition
https://freerepublic.com/focus/f-news/4118337/posts
NONE of which were firearms thefts