If you only steel something in Germany (without weapons or violence) you can receive up to 5 years prison sentence or have to pay penalty. (I had to look this up myself) To your next question: I probably wouldn't accuse anyone for taking something from a shop. But if I would see somebody steeling something valuable like a car or takes it directly from the owner like pickpocketing I would probably accuse the thief.

Like Stozi said it depends on what was stolen but also in which way it was stolen. If weapons were involved or violence then the sentence will be way longer.

The length of their prison sentence will depend on what they stole.