iPhone 5: after damage and screen replacement both cameras are dead

So, I've been asked to repair an iPhone 5 whose user dropped it while riding a motorcycle. To make it even worse, the phone was afterwards run over by a car... As the user explained, they themselves checked the phone, which seemed to be working properly although with an obvious cracked screen.

So the user decided to swap the screen; good so far, the phone was fixed. Well, not yet, since that moment both cameras in the device (although they seem to be physically ok) won't work. The camera app opens perfectly, but it will just show up a dark screen for both rear and front camera.

My question is, bearing in mind that I haven't opened the device yet: should I replace both cameras? (although I think it must be that something went loose) or any other suggestions??