This is an interesting situation. While I don't know what significance the "changed" items are on the forged lease, the important thing is for you to consult with an attorney if there is an attorney's fee provision in the lease.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult with your own attorney.
Forgery is a crime, BUT what are your damages from not having a lease? What money have you lost because of it?
If you can get the District Attorney to prosecute, then I suppose the forger will have criminal liability. There is no civil suit here because you didn't lose any money.