I don't think you're getting the difference quite right. A public interest defense is one that argues that a public interest exception, included in a law, appl

I don't think you're getting the difference quite right. A public interest defense is one that argues that a public interest exception, included in a law, applies. In jurisdictions where a public interest defense is possible, i.e. Canada, it applies only to laws which include it as a public interest exception (in Canada, it would be the Security of Information Act of 2001). If a defense argues that a murder was okay because it was in the public interest, that wouldn't be a public interest defense, because the laws against murder don't include a public interest exception. Arguing that such an exception should be made by the jury, rather than that such an exception in the law applies to your case, is a straightforward argument for jury nullification. In the US, I'm not aware of any laws that include a public interest exception, so a public interest defense would not be possible--appeals to the jury to find someone not guilty because their crime was in the public interest would be appeals for jury nullification. There are a few defenses that work on these sorts of exceptions which only apply to specific laws. For example, truth is a defense against a libel charge but not against a HIPAA violation charge, and self defense is a defense against a murder charge but not against a robbery charge. [1] https://en.wikipedia.org/wiki/Public_interest_defence https://en.wikipedia.org/wiki/Public_interest_defence