Grimulkin

I wonder if anyone can describe to me how box structures such as brief cases, camera cases etc. that are constructed out of medium weight (5-6 oz.) miter cut leather are sewn. Stitching is not visible on inside corner of work as might seem impossible to me. What kind of machine can accomplish this miracle of precision . I have seen items like this and am baffled as to how this is done. I would be most grateful if any old pows out there could enlighten me. Many thanks.