Every criminal case in California starts from the same rule: the prosecution must prove each element of the charge beyond a reasonable doubt, and you do not have to prove anything. A defense is the reason a jury should not be convinced, or the reason the court should not let the case reach a jury.
This guide covers the defenses seen most often in San Diego courtrooms, the rule behind each, and who has to prove what.
Insufficient Evidence and Reasonable Doubt
The most common defense is simply holding the prosecution to its burden. Under Penal Code section 1096 and CALCRIM 220, the jurors must be left with an abiding conviction that the charge is true. If a single element is unproven, the verdict must be not guilty.
It is built through cross-examination and by showing that circumstantial evidence supports an innocent explanation as reasonably as a guilty one. When the evidence is legally insufficient, a motion for acquittal under Penal Code section 1118.1 asks the judge to end the case before it reaches the jury.
Self-Defense and Defense of Others
Self-defense and defense of others are complete defenses to assault, battery, and homicide charges. Under CALCRIM 3470 the jury must acquit if all three elements are present:
- You reasonably believed that you or someone else was in imminent danger of being killed, suffering bodily injury, or being touched unlawfully.
- You reasonably believed that the immediate use of force was necessary to defend against that danger.
- You used no more force than was reasonably necessary to defend against it.
No Duty to Retreat and the Castle Doctrine
The belief must be reasonable, not necessarily correct. Deadly force is justified only against a threat of death or great bodily injury. California imposes no duty to retreat: a person who is attacked may stand their ground and, if reasonably necessary, pursue the attacker until the danger has passed.
Inside the home, Penal Code section 198.5 presumes a reasonable fear of imminent death or great bodily injury when you use force against someone you know or reasonably believe has unlawfully and forcibly entered your residence. Once any evidence of self-defense is before the jury, the prosecution must disprove it beyond a reasonable doubt.
Accident, Lack of Intent, and Consent
Almost every crime requires a mental state. General intent crimes such as battery require only that you intended the act. Specific intent crimes such as theft, burglary, and attempted murder require a further purpose, like the intent to permanently deprive an owner of property. No proof of that mental state, no crime.
Under Penal Code section 26 and CALCRIM 3404, a person is not guilty of an act committed through misfortune or accident, without criminal intent or criminal negligence.
Consent matters where lack of consent is an element. In sexual assault cases under Penal Code section 261, consent means positive cooperation in act or attitude, freely given with knowledge of the nature of the act, and a reasonable good faith belief in consent is also a defense. It is no defense where the person cannot legally consent, as with minors.
Mistaken Identity, Alibi, and False Accusation
Eyewitness misidentification is one of the most frequent causes of wrongful conviction. CALCRIM 315 directs jurors to weigh lighting, distance, stress, the presence of a weapon, cross-racial identification, and delay. Penal Code section 859.7 requires blind administration of lineups and a record of the witness's confidence at the time, and a lineup that ignores those rules can be attacked before trial and before the jury.
Alibi is evidence that you were somewhere else. Under CALCRIM 3400 you do not have to prove it; if it leaves a reasonable doubt about whether you were present, the jury must acquit. Under Penal Code section 1054.3, alibi witnesses generally must be disclosed to the prosecution before trial.
A false accusation defense focuses on the accuser's motive to lie: a custody dispute, a breakup, immigration concerns, money, or a need to explain an injury. Prior inconsistent statements, text messages, and the timing of the report are the tools.
Duress, Necessity, and Entrapment
Duress under Penal Code section 26 and CALCRIM 3402 applies when you acted because of a threat that gave you an actual and reasonable belief that your life was in immediate danger if you refused. Fear of future harm is not enough, and duress is not a defense to murder in California.
Necessity under CALCRIM 3403 is a choice-of-evils defense. You must show you acted in an emergency to prevent a significant harm, had no adequate legal alternative, did not create a greater danger than the one avoided, reasonably believed the act was necessary, and did not substantially contribute to the emergency.
Entrapment under CALCRIM 3408 turns on the conduct of law enforcement, not your character. California applies the objective test from People v. Barraza: was the conduct of the officer or informant likely to induce a normally law-abiding person to commit the offense? Merely providing an opportunity, such as an undercover buy, is not enough, and your predisposition is not the test.
Intoxication and Insanity
Voluntary intoxication is a limited defense. Under Penal Code section 29.4 it is admissible only on whether you actually formed a specific intent, premeditated, deliberated, or acted with express malice. It is no defense to general intent crimes such as battery or DUI. Involuntary intoxication, such as a drugged drink, can be a complete defense.
Insanity is pleaded under Penal Code section 1026 and judged by the M'Naghten standard in Penal Code section 25. You must prove by a preponderance of the evidence that a mental disease or defect left you incapable of knowing the nature of your act or of distinguishing right from wrong. The trial is bifurcated: the jury decides guilt first, then sanity. A verdict of not guilty by reason of insanity leads to state hospital commitment, not release.
Illegal Search and Seizure, Miranda, and Involuntary Statements
Under Penal Code section 1538.5, the defense moves to suppress evidence obtained through an unlawful stop, detention, arrest, search, or warrant. If the motion is granted, the evidence and anything derived from it is excluded, and a drug or weapons case may have nothing left. In felony cases the motion can be brought at the preliminary hearing and, if denied, renewed in superior court; in misdemeanor cases it is heard in the trial court.
Miranda warnings are required before custodial interrogation. A statement taken without them is excluded from the prosecution's case-in-chief but may still impeach you if you testify inconsistently. An involuntary statement is more serious: if a confession was the product of threats, promises of leniency, or coercion, due process bars its use for any purpose. The prosecution must prove voluntariness by a preponderance of the evidence.
Statute of Limitations and Double Jeopardy
A prosecution filed too late must be dismissed. The general periods are one year for most misdemeanors under Penal Code section 802, three years for most felonies under section 801, and six years for felonies punishable by eight years or more in prison under section 800. Section 799 sets no limit for offenses punishable by death or by life in prison, with or without the possibility of parole, for embezzlement of public money, and certain sex offenses committed on or after January 1, 2017. Many exceptions extend or toll these periods, especially for sex crimes and offenses against minors.
Double jeopardy under the Fifth Amendment, article I, section 15 of the California Constitution, and Penal Code section 1023 bars a second prosecution for the same offense after an acquittal or conviction. Jeopardy attaches when the jury is sworn or, in a bench trial, when the first witness is sworn. A hung jury or a mistrial declared for legal necessity permits retrial.
Who Has to Prove a Defense
Most defenses are not something you must prove. A true affirmative defense is one where the law assigns you the burden, usually by a preponderance of the evidence, meaning more likely than not:
- Reasonable doubt, mistaken identity, alibi, accident, and lack of intent: you prove nothing; the prosecution must prove every element beyond a reasonable doubt.
- Self-defense, defense of others, and duress: once some evidence supports the defense, the prosecution must disprove it beyond a reasonable doubt.
- Necessity, entrapment, and insanity: you carry the burden by a preponderance of the evidence.
When Defenses Are Raised in San Diego Criminal Court
Felonies in San Diego County are prosecuted by the District Attorney at the downtown Central Courthouse at 1100 Union Street and the Vista, El Cajon, and Chula Vista branches. Misdemeanors inside the City of San Diego are prosecuted by the City Attorney. Defenses surface at different stages:
- Arraignment: the plea is entered. An insanity plea normally goes in here, and a statute of limitations problem can be raised by demurrer or motion to dismiss.
- Preliminary hearing, in felony cases: the defense cross-examines officers, argues there is no probable cause, and can bring a Penal Code section 1538.5 suppression motion.
- Pretrial motions: a Penal Code section 995 motion to dismiss after the preliminary hearing, suppression motions, motions to exclude statements, and challenges to an identification procedure.
- Trial: reasonable doubt, self-defense, alibi, mistaken identity, intent, and the affirmative defenses are decided by the jury under the court's instructions.
What to Do Next
If you are under investigation or charged, do not discuss the facts with police, the accuser, or anyone on a recorded jail line. Ask for a lawyer and stop talking. Save messages, photos, and receipts, note who saw what happened, and ask nearby businesses to preserve video before it is overwritten.
Marc S. Kohnen has defended clients in San Diego since 2008, has taken cases to jury verdict, and is licensed in state and federal court. The Law Office of Marc S. Kohnen is at 425 Tenth Avenue, downtown near the central courthouse, and is available 24 hours at (619) 398-2500. Every case is different and prior results do not guarantee a similar outcome.
Questions People Ask
What is the strongest defense in a criminal case?
There is no single strongest defense. The most effective one is the defense the evidence in your case supports and the prosecution cannot answer. In practice, the defenses that end cases most often are holding the prosecution to its burden of proof, suppression of evidence from an illegal search, and exclusion of an involuntary statement, because each removes the evidence the case depends on. Self-defense or alibi can be just as decisive when backed by video or an independent witness.
Do I have to prove my defense?
Usually not. The prosecution must prove every element beyond a reasonable doubt, and defenses like alibi, mistaken identity, accident, and lack of intent simply create that doubt. Self-defense and duress shift nothing to you either: once some evidence supports them, the prosecution must disprove them beyond a reasonable doubt. Only a few affirmative defenses assign you a burden, including insanity, necessity, and entrapment, and even then the standard is a preponderance of the evidence.
Can I claim self-defense if I hit first?
Sometimes. Striking first does not automatically forfeit self-defense, because the law allows force when you reasonably believe an attack is imminent; you do not have to wait to be hit. The problem arises when you start or provoke the fight. Under CALCRIM 3471, a person who starts a fight regains the right to self-defense only if they in good faith tried to stop fighting and clearly communicated that, or if they used non-deadly force and the other person responded with sudden deadly force.
What is the difference between an affirmative defense and a regular defense?
A regular defense argues that the prosecution has not proven an element of the crime, such as identity, intent, or the act itself. You carry no burden; you point to the gap. An affirmative defense accepts the act, at least for purposes of the defense, and offers a legal justification or excuse, such as insanity, necessity, or entrapment. For those, California assigns you the burden by a preponderance of the evidence. Self-defense and duress are often called affirmative defenses but do not shift the burden.
Can evidence be thrown out if police searched without a warrant?
Often, yes. A warrantless search is presumed unreasonable under the Fourth Amendment. Once the defense shows in a Penal Code section 1538.5 motion that there was no warrant, the prosecution must prove an exception applied, such as consent, exigent circumstances, a search incident to arrest, or a valid inventory search. If it cannot, the evidence and anything found because of it is suppressed. The good faith and inevitable discovery exceptions can save some evidence.
This guide is general information about California law, not legal advice about any specific case. Legally reviewed by Marc S. Kohnen, Attorney at Law, State Bar of California #255303, defending San Diego since 2008.
Free, confidential case evaluation, available 24 hours at (619) 398-2500.