The Kristin Smart case: Investigators sift through dirt to solve 30-year mystery

Scientists armed with soil vapor detectors and ground-penetrating radar were at the home of the mother of Kristin Smart’s killer for a second day, examining the soil for secrets in the dirt 30 years after she disappeared.

On Thursday, soil engineer Tim Nelligan and former FBI chemist Brian Eckerode, assisted by local soil scientist Steve Hoyt, put a probe down near Susan Flores’ property in the heart of the Arroyo Grande. They were joined by a team of ground radar experts who scanned the highly targeted area, assisting the San Luis Obispo County Sheriff’s by serving a search warrant for the home.

“We’re trying to find answers,” Neiligan said, “We all want to bring Denise and Stan Smart some peace after all these years.”

Susan Flores’ son, Paul Flores, was the last person seen with Smart as the two went to her dorm at Cal State San Luis Obispo after a party on Memorial Day weekend 1996. He was eventually pronounced dead, but his body was never found.

Decades passed before Flores was arrested and tried. He was sentenced to 25 years to life in prison three years ago for killing Smart. But, insisting on his innocence, he never gave away his remains.

For the past three years, Nelligan and his colleagues, working in Susan Flores’s neighbor’s backyard, used vapor samples to detect volatile organic compounds they say may be associated with decaying human remains. Nelligan, an environmental engineer from San Clemente, met Smart in college. He remembers knocking on his house and asking to use his landline.

Nelligan was seen in that yard again this week. He pushed a small instrument known as a soil vapor probe, which has a long straw-like attachment, three to five feet into the earth. Any gases encountered by the probe were captured and collected, then sealed in a canister. The extracted organic compounds can be sent for analysis.

Nelligan said that, as of 2023, they had refined the science and were preparing to publish an academic paper on low-level physical recovery methods in the soil.

But perhaps most importantly, in September 2023, they helped federal investigators in Yakima, Wash., find two bodies, said Tim Perry, a former federal prosecutor and chief of the Department of Homeland Security. One of the bodies, that of a pregnant woman, was found 10 meters away from where their investigation revealed that the bodies were lying when they were working with the Homeland Security Investigations unit, according to Nelligan.

Tim Nelligan drops vapor samples taken from Susan Flores’ neighbor’s backyard into the lab in 2023.

(Brian Eckenrode)

Since then, they have worked with control samples and real corpses buried in the soil at the body farm to further refine their methods. Some of the work led to Wednesday’s warrant for a search of a building in the 500 block of East Branch Street in Arroyo Grande.

San Luis Obispo County Sheriff Ian Parkinson, along with investigators and experts, showed up at the home Wednesday morning after an investigator issued a search warrant for Susan Flores.

“This investigation is related to the disappearance of Kristin Smart,” the Sheriff’s Office said in a statement. “This operation is the result of a search warrant signed by a Superior Court judge. The Sheriff’s Office remains determined to bring Kristin home to them.”

That warranty was based in part on the work of Nelligan’s team. After their initial discovery, the Sheriff’s Office requested additional data and academic research to support their new method of detecting remains using soil vapor.

Although the practice is still in the theoretical research stage, scientists have spent two decades studying the chemical compounds involved in the breakdown of the human body.

Tim Nelligan believes that a soil vapor probe, like the one pictured, could help find the remains of Kristin Smart.

(Christina House/Los Angeles Times)

The San Luis Obispo Sheriff’s Office previously said officials had contacted the FBI about the investigation into the men. The science at the time was unproven and had never been used in any criminal proceedings, but the team told The Times they were confident in their findings.

San Luis Obispo County Dist. Atty Dan Dow said his office has a commitment to the Smart family and this community: to bring Kristin home.

In a statement, Dow said his investigation office and Assistant Dist. He said. Eric Dobroth assisted in obtaining warranty approval.

“While those responsible for Kristin’s death – and those with information on her whereabouts – can provide answers at any time, we are determined to use all available legal tools to locate Kristin’s remains and support her family until she is returned home,” he added.

Paul Flores was arrested by San Luis Obispo County sheriff’s deputies in April 2021 in the murder of Kristin Smart.

(San Luis Obispo County Sheriff’s Office)

The public’s interest is there, too, and kept Smart’s occasional disappearance from the news, but a podcast called “Your Backyard,” started in 2019 by Chris Lambert, shed new light on the cold case.

In November 2019, Nelligan began researching how bodies decompose in soil. Two months later, he hired Shoyt, another Cal Poly grad with a doctorate in environmental science, who had built a soil sampling business on the Central Coast. Eckenrode, a retired FBI scientist and human decomposition expert, joined them in 2021.

Authorities had repeatedly searched the grounds of Paul Flores’ parents’ homes. Sheriff’s deputies even used radar and ground-penetrating cadaver dogs to search Ruben Flores’ property in Arroyo Grande in 2021. No remains were found, but a month later, both Flores men were arrested and charged in connection with Smart’s murder.

In 2023, the three entered the Arroyo Grande house of Susan Flores, a short distance from Ruben Flores. The property has been subject to search warrants in the past – including one stemming from civil suits against the Smart family.

Susan Flores has never been charged in connection with her son’s crimes. During the search three years ago, he insisted that he did not kill Smart and that his family did not know the missing student.

Attorney Harold Mesick, who secured a not guilty verdict in the Ruben Flores cases, told The Times in 2023 that the idea that a body could be in Susan Flores’ backyard is “ridiculous.”