When I worked in a photographic store a young man brought a film in to D&P that I sent to the lab we used to process it, two days later two policemen came into the shop and told me that the lab had contacted them and reported to them that the film had obscene images of a seven year old girl on it, and the man had been arrested.
The girl's father who was a regular customer in my shop (who I knew well) when the police told him about the matter demanded to know who the man was, threatened to kill him, and had to be physically restrained.
A few days later the little girls father indeed came to see me and demanded that I give him the man's name and address, although I liked the guy and felt very sorry for him I was sorely tempted, but I had to tell him the police had warned me I would be prosecuted if I did .