Why did the prosecution not charge?

Question

Many questions on this site ask a question of the form:

• assuming X committed offence Y, why did the prosecution not charge X with offence Y?

E.g. (paraphrasing):

• Why would the U.S. Attorney focus on civil-rights law, rather than laws specific to homicide? For example, why not focus on 18 U.S. Code § 1112 - Manslaughter, where the concept of willfulness is not applicable?
• Why don't US prosecutors press for imprisonment for crime in the banking industry?
• Can a prosecutor decline to press charges?
• What happens if a prosecutor refuses to file charges?
• In the Hush Money case, why was Trump not charged with the "other" crimes?

So: why might the prosecution not charge?

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^{Certainly, if you want to know whether the facts as you understand them make out offence Y in the relevant jurisdiction, that is a different question. Or if you want to know whether offence Y has a limitation period or some other barrier that would prevent charging it, that likewise is a different question. But if you're asking: "looks like X committed Y, and Y was available to be charged, so why wasn't X charged with Y?" - that's what this question covers.}

Answer 1

It might seem circular to answer "why didn't the prosecutor lay charge Y" by referencing prosecutorial discretion.

However, absent the very rare public explanation for a decision to not prosecute, we generally get zero insight into why prosecutorial discretion was exercised a certain way in a particular instance. Instead, we are left with the myriad factors that are always informing a prosecutor's decision. To go further is just a guessing game, which would render any such question too opinion-based.

In many jurisdictions, charging decisions are guided by policy documents. But there are many standard policy and strategic factors that go into charging decisions. At the highest level, these include consideration of the likelihood of conviction and an assessment of the public interest in a prosecution. A good answer by ohwilleke provides many typical circumstances where prosecutors routinely decline to charge.

I would also add the prosecution has a much better sense of their case than we ever do. What looks provable from the outside may have unseen vulnerabilities that are known only to the prosecution team.

Prosecutors may also choose to prosecute a subset of the offences committed by a person in order to keep a trial efficient and simple. This saves time and can avoid unnecessarily complicating things for the jury. Prosecutors will often select a lead charge that subsumes the general sense of "wrongness" that occurred. E.g. where burglary is charged, it is common to leave out attempted theft or theft.