This news article explains that it was a plea bargain deal Tom.   In order to save the government the cost of a trial, he was offered a reduced charge and sentence.   Plea bargains are very common these days, even for major crimes, due to so many local governments being broke around our nation.   The Lane County DA's office does this all the time with local criminals.

His lawyer was going to argue in court that the killing was an accident:  that he only meant to choke her into being unconscious, and not dead.   That sounds like a concocted defense to me, though.   I, myself, would be hard pressed to believe such an excuse unless there was really compelling evidence to back the claim up.