How To Report Cyber Bullying On Twitter?

There is this person who made a twitter account just to bully people. They are basically saying mean things about people through twitter. I was woundering if anybody knew how to notify some authourity to shut the twitter down or something?
They are basically trying to be A from pretty little liars and they are happy to get all of this recognition when they hear people talking about it at school… It’s sick.
P.S. The school administration already knows (I don’t know who told them but they know)
The account was opened on january 25th so it has only been 2 days but whoever it is has hurt several people’s feelings and I don’t want it to get worse.https://twitter.com/#!/ShotStraight <— this is the twitter if you want to check it out