If it's not because the employee just wanted an excuse to assault a minority or just believes minor criminals should be stopped at all costs and with any force necessary, they're probably the type of person who fantasizes about a shooter attacking someplace they're at, or something like that, so they can be the hero and this minor theft is perhaps the closest they will ever come to that.

In all fairness, it could be a combination of three, these characteristics often overlap in people.