DNA Evidence in Los Angeles Sexual Assault Cases

Few forms of forensic proof have altered the landscape of sex-crime litigation as profoundly as DNA in connection with charges such as rape, according to California Penal Code section 261. Properly collected genetic material can support a victim’s account, clear an innocent suspect, or, in some instances, become the key battleground on which a case is won or lost. Yet DNA evidence in Los Angeles sexual assault cases is not infallible, and skillful defense work can expose its weaknesses.

The attorneys at Kraut Law Group Criminal & DUI Lawyers draw on decades of prosecutorial and defense experience within the Los Angeles criminal process to turn cutting-edge science into persuasive courtroom arguments.

• DNA can confirm direct contact between a complainant and an accused, thereby strengthening the State’s case, especially when other evidence is essentially testimonial.
• It can link a single perpetrator to multiple assaults through California’s CODIS-connected databases, increasing the odds of identifying serial offenders.
• Post-conviction DNA testing has exonerated scores of wrongfully convicted people across the country, underscoring its power to correct miscarriages of justice.

Public fascination with shows such as CSI has created what many judges call the “DNA effect”: jurors expect to see genetic proof in every violent-crime trial. A savvy defense lawyer must know how to address those expectations, either by demonstrating why the absence of testing creates reasonable doubt or by dismantling the prosecution’s interpretation of the results.

• Sexual Assault Evidence Kits (SAEKs) are typically gathered within 120 hours of an alleged assault, but the sooner the better to avoid degradation.
• Swabs may come from the victim’s body, clothing, bedding, and any object the police believe was involved.
• Proper chain-of-custody labels, tamper-evident seals, and temperature-controlled storage are crucial; even brief lapses can lead to disputes over contamination.
• California’s Sexual Assault Victims’ DNA Bill of Rights (Penal Code § 680) guarantees that victims receive written notice about kit testing status and, as of January 1, 2024, the right to request that a kit remain untested.
• Laboratories must follow FBI Quality Assurance Standards; failure to do so can render results inadmissible under California Evidence Code § 352.

When the State mishandles any of these steps, the defense gains a fertile avenue for suppression motions that can cripple the prosecution’s case.

• Rapid DNA instruments can generate a short-tandem-repeat (STR) profile in about 90 minutes, allowing detectives to test suspects while memories are still fresh. Police departments in California publicized multiple cold-case arrests in 2024 after deploying Rapid DNA workflows.
• Low Copy Number (LCN) and “touch DNA” techniques enable the development of profiles from just a few dozen skin cells, which is a dramatic but also prone to stochastic dropout, which can exaggerate alleles or create false mixtures.
• Next-generation sequencing (NGS) now utilizes mitochondrial and Y-chromosome markers to identify perpetrators in mixed samples, but the technology is still refining its error rates for courtroom use.
• Probabilistic genotyping software, such as STRmix™ and TrueAllele®, utilizes Bayesian statistics to interpret complex mixtures and has gained judicial acceptance in California appellate rulings.

These advances create both opportunities and hazards; counsel must stay current on peer-reviewed validation studies, internal lab audits, and any limitations noted by the National Institute of Standards and Technology.

• Contamination: DNA is easily transferred by first responders, lab staff, or even other items in an evidence locker.
• Secondary Transfer: genetic material may migrate via shared laundry, household surfaces, or consensual contact, blurring lines between assault and innocent behavior.
• Partial Profiles: When alleles drop out, statisticians may overstate the weight of remaining loci.
• Laboratory Backlogs: delays increase degradation, risking allelic dropout or bacterial interference; although agencies like San Diego PD cleared their backlog in 2024, many California counties still face months-long queues.
• Analyst Bias: blind re-analysis is rare, and technicians aware of case facts may unintentionally steer interpretation toward inculpation.
• Privacy Misuse: Databases built to store suspect DNA sometimes retain victim profiles and use them for unrelated investigations, as a 2022 San Francisco controversy illustrated.

A robust defense strategy spotlights these vulnerabilities through targeted discovery, expert testimony, and meticulous cross-examination.

• Filing motion-in-limine hearings to exclude tainted or unreliable profiles before the jury ever sees them.
• Retaining independent forensic experts to replicate testing, audit chain-of-custody logs, and calculate alternative likelihood ratios.
• Using consent defenses, a DNA match proves contact, not coercion. The defense can contextualize genetic findings with digital messages, witness statements, or medical records demonstrating consensual intimacy.
• Challenging the statistical weight assigned by probabilistic software, courts have acknowledged that changing a single assumption (e.g., number of contributors) can swing the likelihood ratio by several orders of magnitude.
• Highlighting population substructure issues when allele frequency databases underrepresent specific ethnic backgrounds common in Southern California.
• Leveraging post-conviction DNA testing to vacate convictions where trial counsel failed to demand analysis or where newer methods can exclude the defendant.

• Fourth Amendment limits warrantless collection of intimate samples; forced buccal swabs require probable cause and judicial authorization.
• California’s RADS initiative funnels state funding to test all kits within 120 days, ensuring defendants receive timely lab reports to prepare challenges.
• Defense counsel should invoke Brady and Pitchess obligations to obtain laboratory personnel files, quality-control records, and any prior misconduct findings.
• Victims’ growing control over kit testing (SB 464) may result in missing evidence defenses if the government fails to respect a complainant’s election and later tries to destroy or withhold that kit.
• Genetic privacy concerns are prompting proposed federal rules to curb local “shadow” databases; motions grounded in California’s constitutional right to privacy can exclude evidence obtained through overly broad collection.

• Former senior Los Angeles prosecutor Michael Kraut leverages insider knowledge of crime-lab workflows and discovery practices.
• Our firm maintains a network of nationally recognized forensic geneticists, statisticians, and specialists in contamination control.
• We conduct on-site lab inspections when warranted, documenting chain-of-custody gaps with high-resolution video and affidavits.
• Pre-trial motions frequently target:
  • Improper collection procedures (e.g., nonsterile swabs, expired reagents)
  • Statistical overstatements by prosecution experts
  • Undisclosed mixture contributors that inflate inclusion probabilities
• Where DNA appears damaging, we often reframe it to corroborate consensual intimacy, shifting the jury’s focus to the State’s burden of proving force or duress beyond a reasonable doubt.
• Past results include dismissals before arraignment, full acquittals, and substantial charge reductions achieved after exposing flawed genetic interpretations.

At Kraut Law Group Criminal & DUI Lawyers, our mission is to transform intimidating scientific evidence into an asset for the defense.

When prosecutors claim the science is “bullet-proof,” you need a defense team fluent in both the laboratory and the courtroom. Kraut Law Group Criminal & DUI Lawyers stands ready to dissect every allele, every assumption, and every procedural step to protect your freedom and reputation.

Call (323) 464-6453 or use our secure online contact form for a confidential consultation. Your defense begins the moment you choose experienced counsel committed to protecting your freedom and future.