It's called an affirmative defense I think, and it's the worst kind of defense, because you're admitting you did the bad thing; you're just saying you had a good reason.

Self-defense is a good example. Someone assaults you, you hit htem back, they get hurt or die. Are you in the clear?

Maybe. But your attorney will tell you not to even go that far usually. Unless the evidence is air-tight and you're completely fucked, the better play is to aim for reasonable doubt. If there's even a slim chance you didn't do it, if they don't have enough evidence, you SHOULD avoid the conviction. (Of course the US criminal justice system is a joke.)

"Yes this man broke into my house so I shot him" is a harder defense than, "Your honor, no one saw my client shoot the robber. There was no gun found and no shell casing. Anyone could have shot this man."

Does everyone know what happened? Sure. Can they prove it to the degree required to convict? No. So by law (if followed correctly) you cannot be convicted.

In practice it's not that cut and dry and things go sideways all the time. But it's still your best bet.