Can my lawyer represent me if he knows I'm guilty?
Yes. Defense attorneys are ethically bound to zealously represent all clients, the guilty as well as the innocent. Perhaps no one has ever put the duty as eloquently as Henry VIII's soon-to-be-beheaded ex-Chancellor Sir Thomas More, who, before going to the scaffold, insisted, "I'd give the devil the benefit of law, for mine own safety's sake." A vigorous defense is necessary to protect the innocent and to ensure that judges and citizens and not the police have the ultimate power to decide who is guilty of a crime.
Another way of looking at this is that the defense lawyer almost never really knows whether the defendant is guilty of the crime he or she has been charged with. Just because the defendant says he did it doesn't make it so. The defendant may be lying to take the rap for someone he wants to protect, or may be guilty, but guilty of a different and lesser crime than the one being prosecuted by the district attorney. For these reasons, among others, many defense lawyers never ask their clients if they committed the crime. Instead, the lawyer uses the facts to put on the best defense possible and leaves the question of guilt to the judge or jury.
If my lawyer knows I'm guilty, can my lawyer argue at trial that I should be found not guilty?
Yes. The key is the difference between factual guilt (what the defendant did) and legal guilt (what a prosecutor can prove). A good criminal defense lawyer asks not, "What did my client do?" but rather, "What can the government prove?" No matter what the defendant has done, he is not legally guilty until a prosecutor offers enough evidence to persuade a judge or jury to convict. However, the defense lawyer may not lie to the judge or jury by specifically stating that the defendant did not do something the lawyer knows the defendant did do. Rather the lawyer's trial tactics and arguments focus on the government's failure to prove all the elements of the crime.
Defendant a guilty client may mean committing professional suicide.
Criminal defense attorneys may vigorously defend guilty clients, but as a couple of examples make clear, they risk committing professional suicide by doing so. Way back in 1840, Charles Phillips, one of the finest British barristers of his era, defended Benjamin Courvoisier against a charge that Courvoisier brutally murdered his employer, wealthy man-about-town Lord Russell. Courvoisier privately confessed to Phillips that he was guilty. Nevertheless, Phillips's aggressive cross examinations suggested that the police officers were liars and that other members of Lord Russell's staff might have killed him. Courvoisier was convicted and executed. But when it became generally known that Phillips had known that his client was guilty, Phillips became a pariah to the profession and the public.
Moving forward to 2002, San Diego lawyer Steven Feldman got the "Phillips treatment" when he represented David Westerfield, who was charged with molesting and murdering seven-year-old Danielle van Dam. Feldman knew privately that Westerfield was guilty. Nevertheless, at trial Feldman aggressively attacked Danielle's parents. He offered evidence that they frequently invited strangers into their home for sex orgies, and suggested that one of the strangers could have been the killer. Westerfield was convicted and sentenced to death. Yet like Phillips, Feldman was viciously attacked in the media. TV commentators and members of the public called for his disbarment.
Although Phillips and Feldman gave their clients the best defense possible, their experiences suggest that defense lawyers risk their reputations and perhaps their careers when they go all-out for obviously guilty clients.