Cecil has all the answers:
The Straight Dope: Have any millionaires ever been executed in the United States?: "Prosecutors often don't even pursue the death penalty against the rich--think O.J. Simpson, Robert Blake, Phil Spector, and John du Pont (of the chemical du Ponts). You needn't hire a Johnnie Cochran or a Clarence Darrow to get the treatment. An analysis of Georgia cases showed that prosecutors were almost twice as likely to ask for the death penalty when the defendant couldn't afford a lawyer. Nationwide an estimated 90-plus percent of those arrested for capital crimes are too poor to retain experienced private counsel. In Kentucky, a quarter of death row inmates were defended by lawyers who were later disbarred (or resigned to avoid disbarment); other states are similar. A few states have offices dedicated to providing a proper defense for capital defendants, but a Texas jurist summed up the attitude elsewhere: 'The Constitution does not say that the lawyer has to be awake.' So is it cynical to oppose the death penalty on such grounds? Nah. Just realistic."