Stepping in dog poop is usually just bad luck, but for some criminals it's a step toward the slammer.
That's because dog feces pick up DNA-bearing epithelial cells from the colon on their way out. When those feces are found on the shoe of a suspect -- one who claims not to have been anywhere near the scene of a crime where matching poop was found -- a case may be cracked.
These are the clues prized by a tiny, three-person laboratory at the University of California, Davis -- the only accredited forensic lab in the country dealing in animal evidence.
"The shoe scraping I got, I remember, was just enough to cover the top of a pencil top, maybe a millimeter tall," said Teri Kun, a scientist at the forensic lab of UC Davis' Veterinary Genetics Laboratory, recalling a triple-murder case in Indiana in 2000.
"I remember taking it over to Beth (Wictum, the lab's director), saying, 'This is all I got. I don't expect to get results.' But I got a full profile."
The profile from the suspect's shoe matched a sample from the only dog on the property where the slayings occurred. The killer -- who also left behind a shoe print in a poop patty -- is now serving life in prison.
That's one of the more popular tales recounted by the three scientists who run the lab. And they have plenty of experience telling titillating stories for the media -- one 2006 headline blared, "Snoopy's poop scores crime coup" -- because animals and crime together always make for a good yarn.
But despite the coverage and their unique status, they still struggle to get the word out to criminal investigators about what they can offer.
"What I hear the most when I tell people what I do is, 'Wow, you can do that with animals?' " Kun said. "You know, animals have DNA just like humans. We do essentially everything the human labs do. We're just doing it with animals. We're using all the same techniques, all the same tools, just using primers that are specific to dogs, to cats."
Such DNA comparisons can solve a wide range of cases: incidents of animal cruelty, animal attacks on humans, and human crimes like robbery, rape and murder where an animal left a mark behind -- urine, hair, poop, saliva.
"Some studies show you can't go into a house where there's a dog or a cat without picking up some evidence," said Wictum, the lab director.
Unlike in most genetics research involving animals, the samples aren't neatly packaged. They're often whatever scraps are left behind after they've aged, degraded, been cleaned away -- sometimes just enough to extract the clinching DNA.
In one case, a woman's dog relieved itself on the tire of a car belonging to a man who tried to sexually assault her, so that even though she couldn't pick him out of a lineup and he didn't leave semen behind, he was linked to the scene.
And dog hairs recovered from a shower curtain wrapped around a slain 18-year-old girl were connected back to puppies her killer had received as a gift, solving a case that was four years cold.
Wictum, Kun and their colleague Christina Lindquist want to do more. They hope that every time they go to a law enforcement convention and give a presentation, they increase their chance of being hired and put to work.
"What's frustrating right now is we know there are a lot of cold cases out there where there's animal evidence that can be used, and people aren't aware that we can use it," Kun said. "Part of our endeavor in the past few years has been to try and push and get our name out there."
The scientists are uniquely positioned, with access to databases culled from years of research at the wider Veterinary Genetics Lab, which offers services to test animal parentage or find the likelihood of genetic disease. The DNA databases include dogs, cats, horses, cows, llamas, sheep, goats, pigs and alpacas.
"Having that sort of resource in conjunction with your forensics lab is going to be a rare combination to come by," Kun said.
The lab can also settle disputes over cattle ownership. It investigates dogfighting, tracing abused canines back to breeders. And it offers services in civil cases, usually species identification. For $150, the lab can test a meat sample to determine what it is -- a helpful option for restaurateurs who want to make sure they're getting what they paid for.
(Ellen Huet is a San Francisco Chronicle staff writer. E-mail: firstname.lastname@example.org Twitter: @ellenhuet. Distributed by Scripps Howard News Service, www.shns.com.)