It is hard to prove that someone stole something. Even if you saw them it would be your word against theirs. Criminals use their right to silence. If they are caught with the stolen property, they could have purchased it from someone else. They don't have to tell where they got the stolen property. In our legal system a professional criminal has a big advantage.
Everything you say will be used against you and you will never prove your innocence to the police. You don't have to prove your innocence but the court judge or jury (not the police)have to prove your guilt.
Who is pressing charges? Have they served a warrant? If it is just police questioning you, that is not much to worry about. The police seem to be suspicious of everyone. They question and accuse people of things but that is their job.
