From the Locker to the Lab: The Journey of Cold Case Evidence

When a criminal case goes cold, it can feel like a story without an end. But what happens to the crucial evidence collected during the initial investigation? It doesn’t just disappear. Instead, it begins a long, quiet journey, waiting in secure storage for a new lead, a fresh perspective, or a technological breakthrough that could finally bring answers. This is what really happens to evidence in a cold case.

The First Steps: Collection and Initial Analysis

Before a case can go cold, it must first be active. During the initial investigation, forensic teams work meticulously to collect every piece of potential evidence from a crime scene. This can include anything from fingerprints and DNA to weapons, fibers, and documents. Each item is carefully cataloged, photographed, and packaged to prevent contamination. This process establishes the all-important chain of custody, an unbroken record of who has handled the evidence and where it has been.

This evidence is then sent to a crime lab for analysis using the best technology available at the time. Fingerprints are compared against databases, DNA samples are profiled, and ballistics tests are run on firearms. If these initial tests lead to a suspect and a conviction, the evidence’s journey may end there, often kept until all appeals are exhausted. But if leads dry up and the investigation stalls, the case and its evidence enter a new phase.

Going Cold: The Long-Term Preservation

A case is typically declared “cold” when all credible leads have been exhausted and the investigation has been inactive for a significant period, often a year or more, though this varies by jurisdiction. At this point, the physical evidence is transferred from temporary lab storage to a long-term, secure evidence facility.

These are not dusty, forgotten basements. Modern evidence storage facilities are often climate-controlled warehouses designed for one purpose: preservation. The goal is to protect the integrity of each item for years, or even decades.

• Biological Evidence: Items containing DNA, such as bloodstains, hair, or skin cells, are the most sensitive. They are stored in refrigerated or frozen environments to halt the natural process of degradation. A blood-stained shirt, for example, will be carefully dried, packaged in a paper bag (plastic traps moisture, which can destroy DNA), and kept in a cold, dark place.
• Physical Objects: Weapons, tools, and other solid items are stored in secure containers to prevent rust, decay, or cross-contamination. They are meticulously labeled with case numbers and descriptions.
• Documents and Fibers: Paper evidence, like a ransom note, is protected from light and moisture, which can cause ink to fade and paper to break down. Fibers and other trace evidence are kept in sealed containers.

The challenge is immense. Police departments handle thousands of cases, and storage space is limited and expensive. Maintaining the chain of custody remains critical. Every time a box is moved or an item is checked, it must be logged to ensure it will be admissible in court if the case is ever reopened.

The Reawakening: New Technology Breathes Life into Old Cases

For years, evidence may sit untouched. Then, something changes. A new witness might come forward, or a detective with a fresh perspective might decide to review the case file. Most often, however, the catalyst that reopens a cold case is a technological breakthrough. Forensic science is constantly evolving, and a technique that was science fiction 20 years ago might be standard practice today.

This is where the true potential of preserved evidence is unlocked. Cold case detectives can petition to have items re-submitted to the crime lab for testing with these new methods.

DNA and Genetic Genealogy

The most significant game-changer has been the advancement in DNA technology. Early DNA testing required a significant amount of biological material, roughly the size of a quarter. Today, forensic scientists can generate a full DNA profile from just a few skin cells left behind when a person touches an object. This is known as “touch DNA.”

Furthermore, the creation of national DNA databases, like the FBI’s Combined DNA Index System (CODIS), allows law enforcement to compare a DNA profile from a cold case crime scene against millions of profiles from convicted offenders, arrestees, and other crime scenes.

The most recent revolution is investigative genetic genealogy. This is the technique that famously led to the arrest of the Golden State Killer, Joseph James DeAngelo, in 2018. Here’s how it works:

1. Forensic scientists take the unknown DNA profile from the cold case evidence.
2. They create a data file and upload it to public genealogy websites, like GEDmatch or FamilyTreeDNA, where individuals have voluntarily shared their DNA profiles to find relatives.
3. The database searches for partial matches, identifying the unknown person’s distant cousins or other relatives.
4. Genealogists then build out family trees from these matches, working their way forward in time to identify a potential suspect.
5. Once a suspect is identified, police must obtain a new DNA sample from that person (often from a discarded item like a coffee cup) to make a direct comparison and confirm the match.

Other Technological Advances

It’s not just about DNA. Other fields have also seen incredible progress:

• Digital Forensics: Experts can now recover data from old floppy disks, damaged hard drives, and early-generation cell phones that were previously inaccessible.
• Advanced Ballistics: New 3D imaging technology allows for more precise comparisons of markings on bullets and shell casings, linking them to a specific firearm with greater certainty.
• Chemical Analysis: Modern chemical analysis can identify tiny particles of soil, pollen, or industrial materials on a victim’s clothing, potentially linking them to a specific location where the crime occurred.

When a new test yields a positive result, the case is no longer cold. The journey of the evidence enters its final chapter: the courtroom. Prosecutors, defense attorneys, and forensic experts will scrutinize the evidence, the chain of custody, and the new scientific methods used, all in the pursuit of justice that has been waiting for years.

Frequently Asked Questions

Can all old evidence be re-tested? Not always. The viability of evidence depends heavily on how it was collected and stored. If biological evidence was contaminated or allowed to degrade, it may not yield a usable DNA profile. Sometimes, the original testing process destroyed the only sample available.

Who decides to reopen a cold case? This is often done by dedicated cold case units within police departments. A detective might reopen a case based on a new tip, a family’s request for a review, or a systematic effort by the department to apply new technology to unsolved homicides or other serious crimes.

What is the biggest challenge in prosecuting a cold case? Besides the scientific hurdles, the passage of time is the biggest challenge. Witnesses may have died or their memories may have faded. Original investigators may have retired. Proving a case beyond a reasonable doubt with decades-old evidence and testimony can be incredibly difficult for prosecutors.