Jed S. Rakoff in the NYRB (Brittany Murray/Long Beach Press-Telegram/AP Images):
[T]he information-deprived defense lawyer, typically within a few days after the arrest, meets with the overconfident prosecutor, who makes clear that, unless the case can be promptly resolved by a plea bargain, he intends to charge the defendant with the most severe offenses he can prove. Indeed, until late last year, federal prosecutors were under orders from a series of attorney generals to charge the defendant with the most serious charges that could be proved—unless, of course, the defendant was willing to enter into a plea bargain. If, however, the defendant wants to plead guilty, the prosecutor will offer him a considerably reduced charge—but only if the plea is agreed to promptly (thus saving the prosecutor valuable resources). Otherwise, he will charge the maximum, and, while he will not close the door to any later plea bargain, it will be to a higher-level offense than the one offered at the outset of the case.
In this typical situation, the prosecutor has all the advantages. He knows a lot about the case (and, as noted, probably feels more confident about it than he should, since he has only heard from one side), whereas the defense lawyer knows very little. Furthermore, the prosecutor controls the decision to charge the defendant with a crime. Indeed, the law of every US jurisdiction leaves this to the prosecutor’s unfettered discretion; and both the prosecutor and the defense lawyer know that the grand jury, which typically will hear from one side only, is highly likely to approve any charge the prosecutor recommends.
But what really puts the prosecutor in the driver’s seat is the fact that he—because of mandatory minimums, sentencing guidelines (which, though no longer mandatory in the federal system, are still widely followed by most judges), and simply his ability to shape whatever charges are brought—can effectively dictate the sentence by how he publicly describes the offense. For example, the prosecutor can agree with the defense counsel in a federal narcotics case that, if there is a plea bargain, the defendant will only have to plead guilty to the personal sale of a few ounces of heroin, which carries no mandatory minimum and a guidelines range of less than two years; but if the defendant does not plead guilty, he will be charged with the drug conspiracy of which his sale was a small part, a conspiracy involving many kilograms of heroin, which could mean a ten-year mandatory minimum and a guidelines range of twenty years or more. Put another way, it is the prosecutor, not the judge, who effectively exercises the sentencing power, albeit cloaked as a charging decision.
The defense lawyer understands this fully, and so she recognizes that the best outcome for her client is likely to be an early plea bargain, while the prosecutor is still willing to accept a plea to a relatively low-level offense. Indeed, in 2012, the average sentence for federal narcotics defendants who entered into any kind of plea bargain was five years and four months, while the average sentence for defendants who went to trial was sixteen years.