Will an expungement for a petty theft infraction cause an employer to reconsider?

I'm confused about my situation. I was recently offered a full time position after interning and freelancing at a company for 3 months, only to be disqualified for my petty theft infraction almost 10 years ago when I was 19. They have a zero tolerance policy. My direct manager is really pushing for me because I'm regarded as a great worker, and wants me to get it "erased" or expunged, then she said they could hire me. How is that, if the company is already aware of my infraction? Is that possible and how can that make sense