In most every case we see in our court system, if the defendant can afford a lawyer, they do so because they feel as if they have no chance in winning unless they pay for the service. However, in the case of murder, the questions of whether the lawyer knows if his client is guilty or not questions the moral compass of the lawyer. Should it bother the lawyer that they are defending a person guilty or rape, murder, embezzlement etc. ? In my opinion, it takes a certain mindset to do this job. The person in law schooling interested in becoming a defense lawyer has to be aware of the moral decisions he must make in his profession. I am not implying that these decisions are going to ever be easy or morally correct but this is what the profession brings. If a person can handle these situations than it might make them an excellent defense lawyer.
However, a hired defense lawyer's obviously have a choice to let go of the client but if its a public defender they have no choice. Public defenders are assigned to a case and usually have to stay. It is part of a lawyers duty as a job to do what is best for their client, so they cannot try to give up the case. It is like gambling, the lawyer has to take the best shot at the case and it is for his own reputation as well as the well being of his client.
Another interesting suggestion I thought of was what if they client admits they are guilty but could be lying to the lawyer. There have been many cases where people try and take the rap for a loved ones bad doings so that they do not spend the rest of their life in jail. For example, a parents who knows his child committed homicide. In this case, it also doesn't seem beneficial for the defense lawyer to know whether they are guilty or innocent. Even if they get an answer, it could be a lie in either direction. Over all, it is the side that makes the strongest case for the conviction. The way evidence is presented to the jury is a huge aspect of how the verdict comes out. Stronger evidence such as DNA, has become extremely useful in our court systems today. They knowledge of DNA has also broadened due to it being taught during primary schooling and the fact that it is all over crime shows. The awareness of it has grown which makes it more difficult for a murder/ rapist to get away with their crime.