How can the police use Facebook to convict you of a crime?

[Miley Breckyn]

I am writing a research paper on the police use of social media and i cant really find much on the topic. My questions are:
Are there cases challenging the police use of social network sites?
should what they find be admissible for an arrest?
Is it a violation of privacy?
what should officials be allowed to do? Like suspending a student for pictures found on Facebook?

Anything you could tell me would be extremely helpful! I have been searching for days and cant find anything that is exactly these questions answered.

[Evas]

Here are a couple of sites for reference.

[bakebossno1]

Anything you put on FB is public knowledge and anyone including the police can use it against you. If you are doing something embarrassing or immoral use your head and don't brag about on FB. Everyone uses it now, loan companies, process servers, even repossessers track your whereabouts by FB.