How Cops Use Pizza Crusts and Half-Eaten Burgers to Solve Murder Mysteries

Snow was falling in the Oshtemo Township of Western Michigan on January 8, 2015 when a vehicle sped out of the parking lot of the Old National Bank. Shortly after, it took a hard 90-degree turn and became lodged in a snowdrift. Two men emerged from the car and attempted to push it back out onto the street. After a few minutes, they were successful and zoomed off.

That's how one witness, a retired teacher, described the events to local police, after seeing the car careening away from the bank.

As the man described the route of the vehicle, investigators discovered the crash site. They also found the first and only piece of DNA evidence linking one of the men in the vehicle to a series of bank robberies in Western Michigan that had occurred over the course of two years. There, in the clearly marked crash site of the snowbank, was a half-eaten Wendy's cheeseburger, dropped as the two men struggled to dig out their vehicle.

Between May 2014 and January 2015, Dominick Johnson and his half-brother Nathan Benson robbed banks at gunpoint in Galesburg, Comstock Township, and Oshtemo Township. Benson was the stickup man; Johnson, the getaway driver. They were linked to several other failed bank robberies in the region as well.

It was Johnson's DNA that was later determined to be on the cheeseburger. They are both now serving prison sentences for the robberies: 72 years for Johnson, and 14 years for Benson—his sentence was reduced for aiding prosecutors and testifying against his half-brother in court.

In the case, the DNA evidence removed from the food in the snowbank played an important part. It was not the only piece of strong evidence, but it did help prove beyond a reasonable doubt to jurors that Johnson was one of the perpetrators. There was also witness testimony, including Benson's, and cellphone data. Nonetheless, speaking to MUNCHIES from his office at the Department of Justice, US Attorney Patrick A. Miles Jr., who helped prosecute the case, described the DNA evidence as, "very persuasive to a jury."

Johnson's case is one of a few since 2015 in which DNA evidence recovered from food played an important role in obtaining a guilty verdict.

In May of last year, one of the United State's most high-profile murders depended largely on DNA found on a piece of food. The Savopolous murders—a grisly quadruple homicide in Washington, DC—piqued the public's darkest fascination for a variety of reasons: the wealth of the family, the alleged torture of a ten-year-old-boy, and an apparent lack of hard evidence, which seemed to leave the case precariously dependent on a piece of Domino's Pizza recovered from the Savopolous home.

There are still many questions (and conspiracies) about what really happened, but one man, Daron Wynt, was eventually apprehended—his saliva matched the DNA found on the pizza

The use of forensic DNA evidence is not new; it has been utilised since roughly the mid-1980s, but the science behind it has continually gotten better. The intriguing question is why DNA found on food has been popping up in trials with some degree of frequency since 2015.

Has there been some recent procedural or scientific improvement—or is it just a coincidence?

David Foran, the director of the Forensic Science Program at Michigan State University and a qualified expert on forensic DNA profiling, suspects that these cases are most likely due to police procedure, more than anything else. He says that "crime scene investigators have gotten more aware."

"They've been collecting cigarette butts for a long time, but the idea that a piece of food might be evidence, or a piece of gum on the ground, is subtle. They are probably more aware of that now and more willing to collect it."

However, there are also technical elements that have evolved over time that have allowed for DNA testing on food, although it's been a gradual change—not some magic threshold that was crossed in the past few years.

DNA is present in every cell of our bodies (except red blood cells), and any stray cells left behind can potentially be used as evidence. One of the problems that initially existed with this form of testing was that the sample size of genetic material initially had to be quite large.

"Around the OJ [Simpson] trial time was when some of the newer techniques started coming into play," Foran tells me. "Before that, the rule of thumb was that you needed a bloodstain about the size of a nickel to do DNA testing. Nowadays. you can do it on stuff you can't even see."

Foran explains that forensic DNA testing has become generally standardised across the United States, and depends on testing 13 "core locations" on human chromosomes. This type of testing, known as Short Tandem Repeat (STR) analysis compares similarities between forensic evidence and those of a suspect.

"If you have a blood stain at a scene and your suspect has one DNA profile. and the blood is different at all, then you've got the wrong person," says Foran. "If they are the same, if you get the same result at all 13 locations for the evidence at the suspect, then you can do some pretty simple math and say, 'What are the chances that that blood came from someone else besides the suspect?'.

The chances of an innocent person having the exact same DNA profile as a forensic sample are infinitesimally small—which is why it's often described as being as unique as a fingerprint, although, as Foran points out, it's impossible to put a numerical metric on a fingerprint. The computational accuracy of DNA evidence is something juries can easily wrap their heads around.

A DNA sample found on food is inherently more complex than finding a blood or semen stain (two bodily fluids often used as forensic evidence), for a variety of reasons. Saliva is filled with cells from the inside of the mouth, but it is not immediately visible to the human eye the way other fluids can be. Although, Foran notes that if food is recovered, a bite mark will point an investigator directly to the area that needs to be tested.

Another issue is the timeframe of DNA decomposition after it has been left at a crime scene.

Foran says that DNA is relatively stable, but can be affected by its environment—moisture and heat, as with most things, will speed decomposition. But, DNA left on food is potentially vulnerable to other problems as well. Bacteria and fungus will both destroy DNA, so a sample found on food must be processed quickly.

"If stuff starts growing on it, as it easily would on food left out, you're not going to go back to the hamburger on the ground a month later and get DNA off of it. It's just extremely unlikely, but on the other hand, if you can collect it that same day and get it in a refrigerator, then whoever ate that part of that hamburger, their salivary DNA is going to be all over it."

What is important is that the evidence is handled and stored properly on its way to testing. If it is, then food can be a reliable and accurate source of forensic DNA material and—if these recent cases are any indication—an important resource for criminal investigators.

As forensic science and police procedures continue to improve, criminals will also adapt their strategies—though perhaps the best advice to them would be mom's old adage that, when eating, to finish their plate.