Nearly 25 years after the disappearance of the college student Kristin Smart in California, the search for clues in her death has intensified, with investigators using cadaver dogs and ground-penetrating radar on Monday to canvass a property connected to a “prime suspect,” the authorities said.
The San Luis Obispo County Sheriff’s Office said it had obtained a search warrant to comb for evidence at the Arroyo Grande, Calif., home of Ruben Flores, whose son, Paul Flores, was the last person to see Ms. Smart on the day she disappeared in May 1996.
Ms. Smart, a student at California Polytechnic State University in San Luis Obispo, had been walking back to her dorm room from an off-campus party when she vanished. She was 19.
Mr. Flores, a former Cal Poly student who is now 44, has long denied playing a role in her disappearance, but after previously referring to him as a person of interest in Ms. Smart’s death, the sheriff’s office began to declare him a “prime suspect” in the last several months.
“That’s what he is, based on more evidence that’s been collected in the case,” Tony Cipolla, a spokesman for the San Luis Obispo County sheriff, said on Monday in an interview.
The search of Ruben Flores’s property could take up to two days, according to the sheriff’s office.
Mr. Cipolla declined to elaborate on the nature of the evidence because the investigation was continuing and the search warrant was sealed, but he noted that this week’s search of Ruben Flores’s property had been the most extensive one there in the decades-long effort to find Ms. Smart’s remains.
“That’s what we’re investigating, just to see if that’s indeed a possibility,” he said.
Paul Flores did not immediately respond to requests for comment on Monday. A lawyer who previously represented him in the case had retired, and it was not immediately clear whether Mr. Flores had a new lawyer.
A lawyer for his father declined to comment on Monday about the search, citing what he said was a gag order in the case.
The authorities had previously searched the homes of Ruben Flores and Paul Flores, who lives in San Pedro, Calif., along with several other locations. Last year, the authorities said they had seized as evidence two trucks that belonged to members of the Flores family in 1996.
The sheriff’s office also said at the time that it had submitted 37 pieces of evidence collected after Ms. Smart’s disappearance for modern DNA testing.
Ms. Smart’s family commended investigators in a statement on Monday for pursuing new evidence in the case.
“We are encouraged by the news of today’s search of Ruben Flores’s property,” the statement said. “We appreciate the vigilance and professionalism of Sheriff Ian Parkinson and his department and our family looks forward to learning more in the hours and days ahead.”
There have been false hopes of a breakthrough before in the case, however. In 2016, the F.B.I. excavated three sites on a hillside on the Cal Poly campus, but did not find Ms. Smart’s remains. In 2002, her family had her declared legally dead.
After Ms. Smart disappeared, her family filed a wrongful-death lawsuit against Mr. Flores, who the authorities said had told them that he walked Ms. Smart only as far as his dorm, where they parted ways.
Last month, Mr. Flores was arrested by the Los Angeles Police Department on a charge of firearms possession by a felon, The Los Angeles Times reported. He had previously been convicted of driving under the influence, according to public records.
The firearms charge stemmed from evidence obtained by the San Luis Obispo County sheriff last year as part of an earlier search warrant, the authorities said.
The circumstances surrounding Ms. Smart’s disappearance continue to draw national attention, with the CBS true-crime show “48 Hours” dedicating an episode to the languishing case last November.
“Technically, it’s not a cold case,” Mr. Cipolla, the sheriff’s spokesman, said. “It’s still an active case.”
Michael Levenson contributed reporting. Sheelagh McNeill contributed research.