OK, that blows.
So, first of all, the cops -- frets is right. Call. Keep calling. When you become a bigger pain in the ass than a slam-dunk case, they'll give a shit.
If they block you from doing that, go to your local media tip lines -- all of them. Hit them again and again. Sooner or later, one will have a slow news day and will be interested in the cops not wanting to solve a crime that is such a slam dunk. Yes, murders are more important, but come on -- this doesn't even require any real brain power.
In the unlikely event you have renter's insurance, report the theft. Believe me, the insurance company won't want to pay for what the cops can get back, but are just too lazy. THEY are a HUGE pain in the butt.
OK, so you're thinking of breaking lease. Check the landlord tenant laws in PA and Philly. In WA you are jointly and severally responsible for the rent and the apt, whether you live there or not. What that means is, you can move, your roomie can trash the place and skip, and you could end out paying all the rent and damage, and still trying to support your sorry backside somewhere else. That would seriously blow.
Level with your landlord and ask them what your rights are. If they are a professional management company, they may have suggestions I hadn't considered. At the end of the day, you might be stuck just waiting out the lease and then moving, but you don't have to renew -- nobody can make you.
Also, don't forget to check on any utilities that are in your name. Just 'cause it's the electric bill for the apt doesn't mean they wouldn't come after you. If your manager does have a way for you to break lease and run, shut off your utilities and give them the name of the new responsible person. You can't set up the new account, but the power company basically sends a letter that tells the new person what they owe and to get their butt in gear if they like having power.
Now, this is kind of like closing the barn door after the horse, but go to your Local Hardware conglomerate warehouse (Home Depot, Lowes, or whatever the hell you have out there) and buy a front door knob and latch assembly. They lock. Change out the door knob on your bedroom door for the one you bought, the one that locks, and now you can lock your door when you leave. Pay attention to how you take the old one apart and save it so you can reinstall it when you move out.
It never rains, it pours, and it really does suck. I'm sorry it happened to you.