The nature of prosecutorial discretion

All criminal charges are filed at the discretion of a public prosecutor (except in a few states, where private citizens can file misdemeanor criminal complaints, which public prosecutors often have a right to take over). Prosecutors have no legal obligation to file criminal charges even when they have evidence sufficient to prove guilt, and in fact prosecutors routinely decline to prosecute charges even when they have the evidence to do so. See Daniel Richman, Actual Knowledge, Willful Blindness, and the Jan. 6 Hearings, LawFare blog, June 21, 2022:

Make no mistake, no responsible Justice Department prosecutor would restrict her analysis to the law and the facts when deciding whether to bring any criminal case, let alone one against a former president. Considerations of the public interest will regularly counsel against a prosecution, even when the elements of an offense can be proved beyond a reasonable doubt.

Prosecutors decline to prosecute some cases for a wide variety of reasons, and courts as well as scholars routinely affirm that that discretion not to charge offenses is essential to ensure justice. Legally, prosecutors may decline to prosecute for any reason except one prohibited by law, such as electing to charge based on the suspect’s race, ethnicity, religion, or political views and activities. Prosecutors generally have no obligation to explain their charging or non-charging decisions to the public or a court; alleged victims have no standing to challenge prosecutor’s declination (or guilty plea agreement) decisions; and judges have virtually no authority to review or reverse prosecutors’ discretionary charging decisions. See Bordenkircher v. Hayes, 434 U.S. 357, 364 (1978):

In our system, so long as the prosecutor has probable cause to believe that the accused committed an offense defined by statute, the decision whether or not to prosecute, and what charge to file or bring before a grand jury, generally rests entirely in his discretion. Within the limits set by the legislature's constitutionally valid definition of chargeable offenses, "the conscious exercise of some selectivity in enforcement is not, in itself, a federal constitutional violation" so long as "the selection was [not] deliberately based upon an unjustifiable standard such as race, religion, or other arbitrary classification." Oyler v. Boles, 368 U. S. 448, 368 U. S. 456.

See also United States v. Fokker Servs. B.V., 818 F.3d 733, 741 (D.C. Cir. 2016):

The [federal] Executive's primacy in criminal charging decisions is long settled. That authority stems from the Constitution's delegation of "take Care" duties, U.S. Const. art. II, § 3, and the pardon power, id. § 2, to the Executive Branch. See United States v. Armstrong, 517 U.S. 456, 464 (1996 …. Decisions to initiate charges, or to dismiss charges once brought, "lie[] at the core of the Executive's duty to see to the faithful execution of the laws." Cmty. for Creative Non-Violence v. Pierce, 786 F.2d 1199, 1201 (D.C. Cir. 1986). The Supreme Court thus has repeatedly emphasized that "[w]hether to prosecute and what charge to file or bring before a grand jury are decisions that generally rest in the prosecutor's discretion." United States v. Batchelder, 442 U.S. 114, 124 (1979) ….

Correspondingly, "judicial authority is . . . at its most limited" when reviewing the Executive's exercise of discretion over charging determinations. Pierce, 786 F.2d. at 1201 …. The decision whether to prosecute turns on factors such as "the strength of the case, the prosecution's general deterrence value, the [g]overnment's enforcement priorities, and the case's relationship to the [g]overnment's overall enforcement plan." Wayte v. United States, 470 U.S. 598, 607 (1985).

See also Stephanos Bibas, The Need for Prosecutorial Discretion, 19 TEMP. POL. & CIV. RTS. L. REV. 369, 370 (2010) (“Even in a world of unlimited resources and sane criminal codes, discretion would be essential to doing justice. Justice requires not only rules but also fine-grained moral evaluations and distinctions.”); Josh Bowers, Legal Guilt, Normative Innocence, and the Equitable Decision Not to Prosecute, 110 COLUM. L. REV. 1655, 1662–63 (2010) (the notion that prosecutors should rigidly apply the criminal law is “both untenable and unattractive” and almost universally rejected in “case law and commentary”); Zachary S. Price, Enforcement Discretion and Executive Duty, 67 VAND. L. REV. 671, 745 (2014) (“the breadth and depth of substantive [criminal] law . . . presumes a regime in which executive officials exercise discretion to moderate the rigors of statutory prohibitions, thereby creating a law on the ground that more closely approximates popular preferences than the law on the books.”); A.B.A., CRIMINAL JUSTICE STANDARDS FOR THE PROSECUTION FUNCTION, r. 3-1.2(b) (“The prosecutor serves the public interest and should act with integrity and balanced judgment to increase public safety both by pursuing appropriate criminal charges of appropriate severity, and by exercising discretion not to pursue criminal charges in appropriate circumstances.”).

For a recent assessment of a potentially difficult decision whether to prosecute in a high-profile contexts, see Michael S. Schmidt, Is Trump in Legal Peril? This Ex-Prosecutor Would Know, N.Y. Times, July 27, 2022:

… [Former federal prosecutor Andrew Goldstein—one of the lead investigators who examined whether Mr. Trump tried to obstruct the Russia investigation carried out by the special counsel, Robert S. Mueller III— said that even if prosecutors are able to prove all elements against Trump of a criminal charge, mostly likely under 18 U.S.C. § 1512(c) for corruptly obstructing a proceeding of Congress], Attorney General Merrick B. Garland would have an extraordinary decision to make: Is it in the best interests of the country to bring charges against a former president, especially one who may be running again for that office?

Such a prosecution could draw the Justice Department into partisan politics in extraordinary ways. “One of the things that the Department of Justice has to weigh in this kind of a situation is both, what are the potential ramifications of prosecuting, but also the ramifications of not prosecuting,” Mr. Goldstein said.

“And here, in part because of just how high profile all of this is,” he continued, “if there were very clear evidence of a crime and it was sort of very straightforward and provable, but the Department of Justice walked away, there is a real risk of the American people thinking that there are two systems of justice. And that would be devastating to the mission of the department.”

For a state prosecutor's office policy explaining rationales for not prosecuting some wrongdoing, see the Philadelphia District Attorney's Office policy statement on "Alternatives to Incarceration."