Is answering a question you are not sure about under oath perjury?

Question

Suppose I struggle to see at night, but was witness to a crime that took place and have been asked to give testimony. At the stand, I am asked whether I saw the defendant committing the crime, and although I am rather confident I did, I am not sure because the crime took place at night. However, instead of simply saying that, I say 'yes'.

Assuming no one asks me at any point whether I have poor eyesight, have I committed perjury by not explicitly saying that I am not sure?

I admit that this is a bit of a silly example, but it's the first thing that came to mind and sort of demonstrates the point.

So to restate the question:

Is answering a question with a yes or no perjury if you are not sure of your answer? Would that be considered not telling "the whole truth"?

Answer 1

In the United States, the question that determines whether it's perjury is whether or not you believe what you said was true.

Whoever—

(1) having taken an oath..., willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true; or

(2) ... willfully subscribes as true any material matter which he does not believe to be true;

is guilty of perjury.

So if an attorney asks if you saw the defendant, and you believe you saw the defendant, "yes" is generally going to be the correct answer. You're free to qualify your answers or answer questions that weren't put to you, but you aren't obligated to do so. Generally speaking, our adversarial system puts the burden on the defense to ask if you're sure, how the lighting was, whether you were wearing your glasses, whether you were drunk, etc.

Answer 2

The California Penal Code states:

An unqualified statement of that which one does not know to be true is equivalent to a statement of that which one knows to be false.

This appears to mean that, in the case presented in this question, your claim that you saw the defendant is equivalent to you asserting that you know that you saw the defendant, which is false.

Answer 3

As a general rule, be upfront with the lawyer who will be calling you as a witness (in this case the Prosecutor). Let them know about the issue and the level of confidence you have that the guy you fingered was indeed the guy who will be listening to your testimony (give a percent that you believe you were accurate... 90% sure it was that guy).

Also be prepared for the defense to ask you questions about this. The Prosecutor MUST give any possible exculpatory evidence to the defense and cannot have any surprises. So if you have a high doubt that the guy you'll be testifying against was there, you need to let the prosecutor know and trust his/her judgement to use you as a witness.

Answer 4

Yes, it could be deemed perjury regardless of the defense's burden of further scrutiny. The legal definition of perjury is premised on the witness's approach toward the truth, not on who (prosecutor or defense) made the question that was inaccurately answered.

Perjury is typically defined in terms of falsehoods made willfully and knowingly. But it is interesting that it is also defined as "swear[ing] absolutely and falsely in a matter material to the point in issue, whether he believed it or not". Black's Law Dictionary, 4th edition (citing Comm. v. Powell, 2 Metc. [Ky.] 10).

Keep in mind that a prosecutor's (or The People's) interest is to punish the actual criminal and strip him/her of the ability to inflict further harm on the society. Imagine a case where A and B are charged of a crime but only A committed it. If the witness testifies that B committed the crime, it is not implausible (although not imminent either) that a prosecutor/jury/judge could perceive in the witness some irresponsible conduct or an intent to impair the ascertainment of the truth.

In the event that material inconsistencies are identified, the witness might lose credibility and subsequently have a hard time to persuade the fact-finder that he [the witness under oath] did not state a falsehood willfully or recklessly.