It may be hard to develop an example where not providing police with an alibi is in your own best interests. Assume for arguments sake that this is the case.
In the united-states, you are not required to disclose an alibi to the police.
Anyone being questioned by police "has a right to remain silent." Miranda v. Arizona, 384 U.S. 436, 444 (1966).
Depending on when and how you invoke that right, your refusal to speak typically may not be used as evidence against you.
But if you're charged with the crime, you must disclose your alibi to prosecutors, assuming you intend to use it at trial. Criminal Rule 12.1 requires you to give notice of your alibi upon request:
The defendant's notice must state:
(A) each specific place where the defendant claims to have been at the time of the alleged offense; and
(B) the name, address, and telephone number of each alibi witness on whom the defendant intends to rely.
Failure to do so may result in you being prohibited from discussing the alibi at trial.
You are not obliged to say anything to the police. However, suppose you later want to rely on an alibi in court. In that case, adverse inferences can be drawn from the fact that you initially withheld your alibi (see: s34 of the Criminal Justice and Public Order Act 1994).
Although, it is important to stress that you cannot be convicted on the basis of your failure to provide an alibi alone. In Murray v United Kingdom (1996), the European Court of Human Rights said that it would have been a violation of Article 6 of the ECHR (right to a fair trial) if Murray had been convicted on the basis of his silence alone. There is a fundamental presumption of innocence until proven guilty and this would violate that (Article 6(2) ECHR). Therefore, the failure to provide an alibi can, at best, be used as supporting evidence.
You are not obliged to tell the police an alibi.
However, if charged with an offence, there is an obligation to reveal to the prosecution in a timely manner the intention to lead an alibi defence, if you in fact intend to lead such a defence. The details of the disclosure must be sufficient to "to enable the authorities to meaningfully investigate" (R. v. Tomlinson, 2014 ONCA 158, para. 121). This is an exception to the general rule that there is no disclosure obligation on a criminal defendant.
R. v. Tomlinson, 2014 ONCA 158, para. 122:
... failure to provide timely and sufficient notice of alibi does not vitiate the defence. The trier of fact may draw an adverse inference when weighing an alibi that has not been disclosed in a sufficient and timely way. In a jury trial, the presiding judge should instruct the jury that failure to make timely and sufficient disclosure of the alibi is a factor the jury may consider in assessing the weight to be assigned to the alibi.
One typical reason why somebody may not disclose self-exonerating evidence is that they accept punishment for somebody else.
The motive could be to protect a family member; or it may be a transaction like a mobster shielding his boss in exchange for some benefit.
Preventing punishment of a perpetrator is a criminal act though, per §259 of the criminal code:
Wer absichtlich oder wissentlich ganz oder zum Teil vereitelt, daß ein anderer dem Strafgesetz gemäß wegen einer rechtswidrigen Tat bestraft [...] wird, wird mit Freiheitsstrafe bis zu fünf Jahren oder mit Geldstrafe bestraft.
Sentence 6 of that paragraph exempts protecting family members though, following the general German principle that the protection from self-incrimination extends to family members.
In Massachusetts it is a crime to mislead a criminal investigation per General Laws Chapter 268 Section 13B:
Whoever willfully [...] misleads [...] another person who is a [...] investigator [...] with the intent to [...] impede, obstruct, delay, prevent or otherwise interfere with [...] a criminal investigation at any stage shall be punished [by fine or imprisonment].
Withholding evidence that shows that oneself has not committed a crime can probably be interpreted as obstructing the investigation of the crime, especially considering the scenarios in the "germany" section above. (That said, I'd be curious whether anybody has ever been sentenced for that.)
“You have the right to remain silent. Anything you say can and will be held against you In a court of law.” (I never understood the “and will” part. But that’s a different conversation). You can hardly understand the myriad of ways a smart cop can build a case against you. Not just what you say, but what it leads to, how you answer, who it might lead to and what they might say, or how what you say might get misrepresented. A detective once asked me about the circumstances of a false accusation and I said I felt better consulting my family lawyer, and when he got upset I said, look, I want to help, but I just need him to advise me to. And the lawyer told me, tell them nothing, if they could arrest you They already would have. Thanks for the vote of confidence. Anyway later I found out the detective really was just trying to rule me out. But making that easier was neither my job nor my responsibility.
