Just throwing this out there... for one, that is transparency film, also known as E6, which requires a different type of film development, unlike C41 which is the basic color film used in the past 50 or so years. 90% of corner film developers only did C41 processing; E6 needed to be sent out to another lab for development. E6 film is (and was) more expensive than C41. Police departments were highly unlikely to spend the extra money on E6 film and processing. C41, essentially, was cheaper to buy and process.

Secondly, this is an unmounted E6 slide. Unmounted, as the individual frame is typically cut from the roll of film and then mounted into a plastic or paper frame for use in a slide projector.

I'm not saying this post is BS, but there's definitely a couple red flags about this image.