The first thing the prosecutor looks for is a legally sound case, or one without any obvious defects that will get it thrown out of court, such as violations of the defendant’s constitutional rights or destruction of evidence crucial to the defense. The prosecutor next decides if there is enough evidence, with regard to both the quantity and the quality thereof, to make conviction probable. Finally, the prosecutor decides if prosecuting the case fits in with the office’s policy objectives, or whether a more informal disposition, like drug counseling or treatment, may be in order.
In reality, if you are charged with a drug case, you will likely be indicted and the case will proceed. If there was an unlawful stop or search, I will prepare and argue a Motion to Suppress Evidence to attempt to get the evidence thrown out.
Even a teeny tiny amount of dope (imagine 1/10 of a Sweet-N-Low packet) will result in a felony charge.