Can I sue a co-signer on a lease?

Can I sue someone who co-signed a rental agreement? I had an apartment with a friend of mine who turned into a total jerk after moving in. I left after a few months and he sued me for the remainder of my half of the rent. His Dad also signed the lease with us, but never paid a thing because he never actually lived there. Neither did I for part of the term, and I was found liable simply because I was on the lease. The jerk even had a replacement roommate off the books, but I couldn't prove that in court! "No evidence" meant "didn't happen." I don't think the lease differentiates the difference between us. Can I sue him for half of one third of the rental term to recoop my damages, and cite the previous ruling as precedent?