Every criminal trial in California starts from the same place: you are presumed innocent, and the prosecution must prove each element of each charge beyond a reasonable doubt. That standard is a jury instruction the judge reads aloud, and it is the measuring stick twelve people use in the deliberation room.
Reasonable doubt is rarely created by one dramatic moment. It is built piece by piece: in the way each witness is questioned, in the gaps the defense exposes in the investigation, and in a closing argument that ties those gaps to the instruction the jury will be given.
This guide explains what the standard means and the steps a careful defense uses to build it. The Law Office of Marc S. Kohnen has defended people in San Diego since 2008 and has taken cases to jury verdict.
What does reasonable doubt mean in California?
California juries are instructed with CALCRIM 220. In plain terms, proof beyond a reasonable doubt is proof that leaves the juror with an abiding conviction that the charge is true. The same instruction says the evidence does not have to eliminate all possible doubt, because everything in life is open to some possible or imaginary doubt. The statutory definition appears in Penal Code section 1096.
Two words carry the weight. Abiding means a conviction that is settled and lasts, not a first impression that could shift on reflection. Reasonable means the doubt must come from the evidence or the lack of evidence, not from speculation. A juror who thinks the defendant probably did it, or even very likely did it, has not reached the standard and must vote not guilty.
The presumption of innocence and a burden that never shifts
The presumption of innocence stays with you through the last word of deliberations. The burden of proof rests on the prosecution for every element of every count, and it never moves to the defense. Each step below is a way of testing whether the prosecution carried its burden, not a way of proving innocence.
Step 1: Challenge the credibility of the prosecution's witnesses
Most criminal cases rise or fall on human testimony, and human testimony is fallible. Evidence Code section 780 lists the factors a jury may consider in deciding whether to believe a witness, and CALCRIM 226 puts those factors in front of the jury. The defense uses the same list as a roadmap for cross-examination.
- Ability to perceive: A bar patron six drinks in and looking at a phone is not the same witness as a sober bystander ten feet away.
- Bias, interest, and motive: An accomplice testifying under a plea deal, a co-worker competing for the same promotion, or a former partner in a custody dispute all have reasons to shade the truth.
- Prior inconsistent statements: What did the witness tell the 911 dispatcher, the first officer, the detective, and the preliminary hearing? If the story grew more certain and more detailed each time, the jury is entitled to ask why.
- Memory and time: A witness is asked to repeat the exact words of a threat from eighteen months earlier.
- Character for honesty: Prior conduct involving dishonesty may be used to impeach a witness, subject to the court's ruling under Evidence Code section 352.
Cross-examination discipline
Cross-examination builds doubt only when it is controlled: questions that suggest the answer, one fact per question, nothing the lawyer does not already know the answer to, and no invitation for the witness to repeat the direct examination. The goal is a handful of admissions that will be quoted in closing. A cross-examination that wanders gives the witness a second chance to persuade the jury and hands the prosecutor material for redirect.
Step 2: Expose weaknesses in the physical and forensic evidence
Jurors arrive with television expectations about forensic science. The defense replaces those expectations with the actual limits of each technique and the actual handling of each item in this case.
- Chain of custody: An evidence envelope logged out for three days with no explanation, a swab stored in a hot patrol car trunk, or a property tag that does not match the report all give the jury reason to question what was tested.
- Laboratory error and procedure: Crime labs have documented contamination events and analyst errors. Bench notes, proficiency records, and quality-assurance files obtained through discovery can show a result was less certain than the final report implies.
- DNA mixtures and low-level samples: A single-source match is powerful. A three-person mixture from a doorknob in a shared apartment is not, and the presence of DNA says nothing about when or how it was deposited.
- Fingerprint limits: Latent print comparison depends on examiner judgment, and national scientific reviews have criticized the field for overstating certainty. A partial print with few points of comparison is fair ground for doubt.
- Chemical testing: In a Vehicle Code section 23152 case, breath device calibration records, the timing of the blood draw, preservative and refrigeration logs, and retrograde extrapolation assumptions can all be challenged.
Step 3: Attack unreliable eyewitness identification
Mistaken eyewitness identification is one of the most common causes of wrongful convictions later exposed by DNA. CALCRIM 315 gives jurors factors to weigh: how well the witness could see, how much stress they were under, whether a weapon was present, how much time passed, whether the witness and the defendant are of different races, and whether anything about the procedure suggested the answer.
A nighttime robbery lasting twenty seconds, viewed across a parking lot while the witness stared at a handgun, is where memory is least reliable. If the witness then picked the defendant from a six-pack photo lineup in which he was the only person with a facial tattoo, or after an officer said something that confirmed the choice, the identification was suggestive and the jury should hear it.
Cross-racial identification deserves specific attention because research consistently shows people are less accurate at identifying strangers of a different race. Confidence at trial is not a reliable measure of accuracy, particularly when it grew after the witness learned the person chosen had been arrested.
Step 4: Offer alternative explanations consistent with innocence
Jurors do not need to believe an alternative explanation is true, only that it is reasonable. CALCRIM 224 tells the jury that when circumstantial evidence supports two reasonable conclusions, one pointing to guilt and one to innocence, it must accept the one pointing to innocence. The defense builds the record to trigger that instruction.
Examples: a defendant's fingerprints inside a car he rode in the week before the theft; text messages that read as threatening alone but sit inside a longer joking exchange; presence at a scene that is also his own block. None of these proves innocence, and none has to.
Evidence that someone else committed the offense, called third-party culpability evidence, is admissible in California if it is capable of raising a reasonable doubt. Motive or opportunity alone is not enough, but evidence linking another person to the crime can be.
Step 5: Use defense expert witnesses
Under Evidence Code section 720 the defense may call its own qualified witnesses to explain the limits of the government's science and offer a competing reading of the same data.
A memory researcher can explain why the identification in Step 3 is unreliable. A forensic toxicologist can show why a blood alcohol result taken ninety minutes after driving does not establish the level while driving. Expert testimony works when it is narrow and concedes what is true, then explains precisely where the prosecution's conclusion outruns the data.
Step 6: Expose police misconduct and investigative gaps
An investigation that skipped steps is itself evidence. If officers did not canvass for other witnesses, did not request surveillance video before it was overwritten, or never interviewed the person the defendant named, the jury may ask what that work would have shown. The defense does not have to prove the answer, only that the question was never asked.
Several tools support this step. A Pitchess motion under Evidence Code sections 1043 and 1045 asks the court to review an officer's personnel file for prior complaints of dishonesty or fabricated reports, and Penal Code section 832.7 now makes certain misconduct records public. A suppression motion under Penal Code section 1538.5 asks the court to exclude evidence obtained through an unlawful stop, search, or arrest; if granted, the prosecution may lose the evidence it needs to proceed. Penal Code section 1054.1 and Brady v. Maryland also require the prosecution to disclose evidence that helps the defense.
Body-worn cameras have changed this analysis. San Diego Police officers and Sheriff's deputies generally record their contacts. When a recording contradicts a report, the report loses its value. When the camera was off at the moment that matters, or footage of a critical interview does not exist, the jury is entitled to wonder why.
Step 7: Decide carefully whether the defendant testifies
You have an absolute right not to testify under the Fifth Amendment and article I, section 15 of the California Constitution. If you do not, the judge instructs the jury under CALCRIM 355 that it may not consider that fact for any purpose, and the prosecutor may not comment on it. The decision is yours alone, made with your lawyer's advice.
Testifying can build doubt when only the defendant can explain a fact the prosecution left unexplained, or when the case turns on intent. It carries risk: cross-examination, impeachment with prior convictions involving moral turpitude, and the tendency of jurors to ask whether they believed the defendant rather than whether the prosecution proved its case. Often the stronger path is to build doubt through the prosecution's own witnesses, and that choice is made late, after the prosecution has rested.
Step 8: Win the jury instructions and use them in closing argument
Before closing arguments, the judge and lawyers settle the instructions. The defense requests instructions on lesser included offenses, the circumstantial evidence rule in CALCRIM 224 and 225, eyewitness factors under CALCRIM 315, and any defense the evidence supports. Each instruction given becomes a rule the defense can quote.
Under Penal Code section 1093 the prosecution argues first, the defense second, and the prosecution rebuts last, so the defense closing must anticipate the rebuttal. The strongest defense closings are organized around the elements: here is what the prosecution had to prove, here is the evidence on that element, and here is the specific reason a juror cannot hold an abiding conviction about it. Doubt argued in the abstract is easy for a prosecutor to wave away in rebuttal. Doubt tied to a named witness, a specific exhibit, and a quoted instruction is not.
Step 9: Unanimity, hung juries, and retrial in California
A California criminal verdict must be unanimous. Article I, section 16 of the state constitution provides for a jury of twelve in felony trials, and twelve in misdemeanor trials unless the parties agree to fewer, and CALCRIM 3550 instructs that all twelve must agree on each count. One juror who holds an honest, evidence-based doubt prevents a conviction.
When the jury reports it cannot agree, the judge may ask whether further deliberation would help but cannot pressure a holdout. If there is no reasonable probability of agreement, the jury is discharged under Penal Code section 1140 and the result is a mistrial, commonly called a hung jury. That is not an acquittal; Penal Code section 1141 permits a retrial. The prosecuting office then decides whether to retry, offer a resolution reflecting the weakness the first jury revealed, or ask the court to dismiss under Penal Code section 1385. Every case is different and prior results do not guarantee a similar outcome.
What to do now if you are facing charges in San Diego
Reasonable doubt is built from evidence, and evidence disappears quickly. Surveillance systems overwrite footage in days, witnesses move, and phone records have retention limits. The steps above work only when the investigation starts early.
Do not give a statement to police without a lawyer present, no matter how informal it seems. Do not discuss the case on jail phones, by text, or on social media. Write down who was present and what you remember while it is fresh. Save messages, receipts, and photographs and give them to your lawyer rather than deleting anything.
The Law Office of Marc S. Kohnen is at 425 Tenth Avenue in downtown San Diego, near the Central Courthouse, and handles cases there, at the Vista, El Cajon and Chula Vista branches, and in federal court. Marc S. Kohnen has defended San Diego clients since 2008 and is available 24 hours a day at (619) 398-2500.
Questions People Ask
What are examples of reasonable doubt?
Reasonable doubt comes from the evidence or the absence of evidence. Common examples include an eyewitness who identified the defendant at night from a distance through a suggestive lineup; a key witness whose account grew each time it was retold or who is testifying under a plea deal; a DNA mixture from a shared surface that cannot be tied to a time or an act; a break in the chain of custody for the item tested; missing body-camera footage of the critical interview; or circumstantial evidence that fits an innocent explanation as well as a guilty one. Under CALCRIM 224, when both readings are reasonable, the jury must choose innocence.
What percentage is beyond a reasonable doubt?
There is no percentage, and California judges will not give the jury one. CALCRIM 220 defines the standard in words: proof that leaves the juror with an abiding conviction that the charge is true. Courts have disapproved of attempts to quantify it, because a number invites jurors to treat the decision as a probability estimate rather than a lasting, evidence-based conviction. What can be said is that it is higher than the preponderance standard used in civil cases and higher than the clear and convincing standard used in some other proceedings. A juror who believes the defendant is probably guilty, or even very likely guilty, has not reached it.
Does the defendant have to prove anything?
No. The burden of proof rests entirely on the prosecution for every element of every charge, and it never shifts. You do not have to testify, call witnesses, present an alibi, or explain the evidence, and the jury is instructed that a decision not to testify cannot be considered for any purpose. A few defenses require the defendant to raise an issue with some evidence before the jury considers it, and insanity is a defense the defendant must prove, but for guilt itself the rule is simple: the prosecution proves the case beyond a reasonable doubt or the verdict is not guilty.
What happens if the jury cannot agree?
A California criminal verdict requires all twelve jurors to agree. If they report a deadlock, the judge may ask whether more deliberation would help but cannot coerce a verdict. When the court finds no reasonable probability of agreement, it discharges the jury under Penal Code section 1140 and declares a mistrial, often called a hung jury. That is not an acquittal, and Penal Code section 1141 allows the prosecution to retry the case. The prosecuting office then decides whether to retry, offer a resolution reflecting the weakness the first jury exposed, or move to dismiss under Penal Code section 1385. The vote split often drives that decision.
Can reasonable doubt come from the prosecution's own witnesses?
Yes, and in many trials that is where most of it comes from. The defense is not required to call anyone. Cross-examination of the prosecution's witnesses can establish poor lighting, distance, intoxication, bias, inconsistent prior statements, or that a critical investigative step was never taken. The prosecution's own criminalist can be asked to concede the limits of a DNA mixture or a partial print, and the arresting officer can be confronted with the body-camera recording or the absence of one. Tied to the reasonable doubt instruction in closing, those admissions give the jury reasons for doubt that came entirely from the government's side of the courtroom.
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.
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