Suppose a perjury case hinges on the interpretation of a single sentence of testimony containing a double negative. Is this sentence given strict boolean interpretation when it favors the defendent? Has this been covered by case law?

For example, suppose a man is tried for murder. In court testimony, when asked the question, "Did you kill Bill Smith?", he replies, "I didn't kill nobody." The man is found "not guilty." Later, new irrefutable evidence becomes available that he killed Bill Smith, so the man is then tried for perjury. The man's defence to perjury is that he indeed said that he killed somebody.
HI aruzinsky,
Has this been covered by case law?

Case law of which country?

I think perjury also applies to misleading statements. That said, the meaning of "I didn't kill nobody" is pretty clear. In this case, two negatives don't add up to a positive.
Quite apart from the linguistic aspect, the law of England (I cannot speak for anywhere else) has the "double indemnity" rule, which means that you cannot be tried twice on the same facts. This extends, I believe, to being tried for perjury when you have denied the offence of which you were originally accused.

Should a court have to rule on the meaning of "I did not kill nobody" or some similar phrase, the "ordinary" meaning of the words would be taken. For a person who regularly uses double negatives the meaning is clear: the standard English equivalent is "I did not kill anybody". A person whose speech follows standard English who argued that he meant "I killed somebody" is likely to get convicted for being too clever for his own good.

Some languages (notably French and Spanish of the languages that I know) regularly use double negatives and in my idle moments I have often wondered how the logical concept of double negation is taught to French and Spanish speakers.
Teachers: We supply a list of EFL job vacancies

Case law of which country?

Preferably, USA.
 Forbes's reply was promoted to an answer.
Site Hint: Check out our list of pronunciation videos.