I watch some of those BBC detective shows, and am continually amazed at the amount of surveillance cameras that seem to be present in large English cities. I'm sure it is inflated, and over-convenient for these shows, but it does seem to be something not out of the ordinary. In the US there are obviously more all the time, but still nothing close to the coverage it seems may exist in England.
I'd imagine that detectives have logged many hours going practically door to door among Midlothian's thoroughfares and businesses trying to get all the video they can from the time frame. Now there's a time consuming chore full of drudgery and disappointment. Even with careful planning, its hard to anticipate where a camera might catch some video of a car on those quiet streets. While not conclusive, simply an image of a car matching a suspect out at 0400 is going to be helpful.
Its not going to be easy. Most video you do find is poor at night, and worse in the rain. It would be a major breakdown in planning to drive into a top-notch convenience store, etc, but people do idiotic things. The best case would be driving somewhere near a Walmart. They have fantastic video all over the place.