Criminal Procedure and Criminal Law Fundamentals
Elements of criminal liability
Criminal liability requires a prohibited act (actus reus) and a culpable mental state (mens rea), with concurrence and causation. The principle of legality forbids punishment without a pre-existing law. Defenses include self-defense, necessity, duress, infancy, and insanity; the burden and standard for each vary.
Investigation and trial
Police may arrest with or without a warrant under defined exceptions, but detention requires judicial review. The prosecutor decides whether to charge. At trial the prosecution bears the burden of proving guilt beyond a reasonable doubt; the defendant has a privilege against self-incrimination. Evidence obtained unlawfully may be excluded.
Worked example. D is charged with assault after pushing V during an argument. D claims V swung first. Self-defense requires an imminent unlawful attack, a reasonable belief in the need for force, and proportionality. If D used force after V retreated, the defense fails; if D honestly and reasonably feared imminent harm and used only necessary force, it may succeed. The prosecution must disprove the defense beyond reasonable doubt.
Traps
- Confusing arrest with formal charge; an arrest is not a conviction.
- Assuming silence at arrest proves guilt.
- Treating self-defense as available against a verbal threat alone.
- Forgetting that the burden of disproving a defense may fall on the prosecution.