Using Forensics in Cold Cases

J. Warner Wallace stands next to a picture of himself as a SWAT officer.
J. Warner Wallace served in the patrol, gangs, narcotics, surveillance, SWAT and cold case units in Los Angeles County.

A Los Angeles County cold case detective shared insights with Sam Houston State University students on how to use forensics to solve criminal cases.

J. Warner Wallace, a 25-year veteran who has served in the patrol, gangs, narcotics, surveillance, SWAT and cold case units, recently shared his career experiences with chemistry classes in the Department of Forensic Science. He used real life cases from his career -- some featured on Dateline, Court TV and Fox News -- to demonstrate the wide array of forensic evidence that can be used to help successfully prosecute homicide cases.

“You have to show the jury the difference between possible and reasonable,” said Wallace. “Anything is possible, but possible doesn’t matter. Everything is possible, but not everything is reasonable. We tell the jury possible is just speculation. Reasonable is an inference that can be drawn from the evidence.”

Picture of a masked burglar with a flashlight.Wallace illustrated how to build a successful prosecution mainly using the case of a husband who was convicted of beating his wife to death with a baseball bat. The case was based on eight pieces of indirect, circumstantial evidence, even though the husband claimed that he was at work at the time of the crime.

“All we’re trying to do is to lock down the evidence,” said Wallace. “Each is a small piece in a large case.”
There was an eyewitness in the case, a neighbor who saw a masked man beat the woman in her home. The neighbor, who had known the family for years, testified that the “burglar” was of the same build as the husband.

To debunk the alibi, Wallace used a video enhancement expert to analyze a videotape, which allegedly showed the suspect at work. The expert focused on the patterns on the man’s plaid shirt in the video to determine it was not the suspect. “Plaid shirts are like fingerprints,” Wallace said. “Each one is different. Look at the button line, where the plaid is sewn, and the seams.”

fingerprintWallace said counters and other surfaces should be checked for DNA samples, both from skin and aspiration. Wallace said it is hard to get skin cell DNA samples from smooth surfaces, but this sort of DNA tends to cling to rougher surface. Fingerprints can be left on many surfaces, including paper, and there are various processes that can be used to retrieve them.

One of the key benefits of the Los Angeles crime lab was a criminologist dedicated to cold cases. The staff member’s top priority was to quickly process detectives’ requests, although during slow periods, the criminologists would work on other crime cases.

With physical evidence, detectives may use serology testing to detect the presence of blood, chemical testing to identify a lubricant on a body, and materials testing on items like the bat in the case to show unique nicks and dents as well as whether the bat was cleaned with bleach. “How many people bleach their bats?” Wallace asked.

Worn baseball bat.Luminal is a substance that can be used to detect blood, bleach or cleaning fluid. In this murder case, the suspect had dirty pants, but luminal showed he had spot cleaned a small area.

In this case, there was no sign of forced entry into the house and only two keys existed. One belonged to the boyfriend and the other to his mother. The key can be dusted for fingerprints or swiped for DNA. In addition, a lock expert can be brought in to show the unique features of the key.

During the interview process, the suspect was very nervous and described an up-and-down relationship with the victim. He admitted to slapping the victim around in the past and threatening to kill her. The statement can be subject to a forensic analysis, which may or may not be admitted in court, but provides clues in the case. “They can tell us if the statement shows deception,” Wallace said. “The suspect might omit the name of his wife or use pronouns. They may say the wife instead of my wife.”

Photo of man's hand writing a statement.In the murder case, the suspect left a suicide note and, although he did not confess to the crime, he indicated he was distraught over something that had happened on the evening of the attack. A handwriting expert can be used to link the suspect to the note and the paper could yield DNA or fingerprint evidence.
Finally, the suspect had an unusual car, a yellow Volkwagon Karmann Ghia, which was seen driving away the crime scene. A car expert was brought in to testify about the rarity of the vehicle and the limited number of vehicles in the area.

In this case, the evidence added up to murder. “We argued to the jury that his innocence is possible, but his innocence was not reasonable,” Wallace said.

In cold cases, Wallace sometimes brought in a behavioral psychologist, who analyzed the scene for clues. This may help confirm if detectives are on the right track with a suspect or may send the case in a specific direction.

Shoes also can provide valuable information in some cases, either by the uniqueness of the brand or a distinctive wear pattern. A materials comparison expert can help with those issues.

During his career, Wallace discovered people with unique expertise. For example, he once used spectrography to analyze the foam pattern from the inside of a shoe, which was identical to one found at a murder scene, with one variation. He used another expert to show how storing the material for 30 years in plastic created the anomaly.

Wallace said that the “CSI effect” is a real issue is in criminal cases, where jurors believe that crimes can be solved in an hour and one person tackles all forensic evidence at all stages in the case because that the way it happens on the TV show. He makes sure jurors know the difference between possible and reasonable and that they are not bothered by unanswered questions before they are selected.

“Cold case units are rare,” said Wallace. “A case can become cold in one or two years. It is when you run out of things you can do. But relationships change and suspects say something to someone. You have to start by looking through the case logically to make the case.”

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