Manta, in all fairness, most other countries have, in some ways, a more reasonable legal system than we have in the United States.
We have an adversarial system, where prosecutors are tasked with, and rewarded for, getting a conviction. There are some limits; for instance, they have to disclose exculpatory evidence (and when they don't and are caught, there are usually consequences), but they are not expected to try to ensure that justice is done; they are expected to get convictions. "Justice" is up to juries (often stupid, poorly informed, or disinterested) or judges, relying on cherry-picked legal citations (because like the UK we have a common law system relying heavily on case law, not a simpler civil law system).
Prosecutors often aspire to political office, which can affect their actions.
This is not a good legal system to have when the government makes more things illegal and conducts increasingly intrusive domestic surveillance. Have you seen this?
http://www.youtube.com/watch?v=6wXkI4t7nuc