83MONTESS is right. Do not declare bankruptcy. First thing, taxes are not dischargeable on a bankruptcy, so they can still come after you anyway. I know people who have gone through this. It's time (actually a lot of time), even more patience, but you can come out on top. Take a moment, gather yourself together, and start looking for a good tax attorney. Start doing as much of the work as you can on your own. I had an attempt at stealing my bank info a few years back. I am a controller (which is a level higher than bookkeeper) so I am always on top of bank stuff. I caught it almost as it happened, notified the bank, police where it took place, police in my town, and the places the transaction were happening. The result was everyone working together, the stores gave the video to the police on the spot, the people where caught, and I had the thousands they took from me back in my account that night. From there I was out of it and the bank handled it. Do as much legwork as you can to investigate who did this, and how. Put stuff together, make a timeline, call anyplace you now of they bought stuff from, get descriptions, video, anything (you'll need to contact local PD to get video - most stores don't give it up easily). If the places are local however they may let you come down and look for yourself - I've been able to do that before when researching possible embezzlement for clients. The more you do, the easier it will be for a tax attorney to represent you, and the less it will cost. He's going to do all this stuff anyway. I am working on a similar case for my neighbor now - not identity theft but they claim he owes $13k in back taxes. It's an obvious IRS error. They make mistakes too.
Good luck - don't give up, and fight the system!