I moved into my apartment and signed a lease on September 12, 2007. On September 25 and 27, there were two assaults on the property where two people almost died because they were beaten by someone with a hammer. I am new to PA and to living by myself (I am a single woman) and this scared me. I received a letter on Sept 28 from the management company of my apartment telling me "to be aware of my surroundings and that the police were investigating". Never heard anything else about it. There are lights everywhere but two bushes are on the side of each entrance door that someone could easily hide behind.

I work odd hours as a hotel manager, sometimes early morning or late at night, and this made me quite nervous. I want to move out and break my lease (I have only lived there for a month and a half). Do I have an out? Can anyone give me advice on what I should do?

If I were you, I'd sign up for self-defense courses. Yes, two people were attacked at your complex. But, unless you somehow managed to wind up in the bad side of town, if you move it will be possible that the same thing has or could happen there. Then what? Do you move again? You can never be sure of being safe where ever you go. So... self-defense courses, so that IF something does happen, you will be better able to protect yourself. Heck, concealed weapon licence, if that's legal in your state and more of your thing. If you are concerned about someone breaking into your apartment, there are several relatively inexpensive things that you can do to make the surroundings more secure (pin locks, dowel rods in sliding door tracks, that kind of thing.) You may want to talk to your apartment manager and get permission to add those (they will probably let you, since it would be a fixture that would improve the place, and who's going to complain about that?).

And you might be able to talk to the police, tell them that you live in the area where it happened and see if they have any update that they can tell you. It's quite possible that this was a targeted attack, and not someone out looking for random victims. Most assaults involve people who have some sort of history, not a stranger jumping out of the bushes.

No this is not grounds to break your lease, crime happens everywhere, this time in your area, next time in another place you could move.
YOU may consder seeing if the bushes can be removed