A California sheriff said on Friday that investigators had found soil evidence suggesting that human remains were once present outside a home connected to the man convicted of murdering Kristin Smart, a 19-year-old who went missing in 1996 after a college party.

On Wednesday, investigators with the San Luis Obispo County Sheriff’s Office began collecting soil samples and taking ground radar scans in the backyard of a home in Arroyo Grande, Calif., about 15 minutes south of San Luis Obispo. The residence belongs to Susan Flores, whose son, Paul Flores, was convicted in 2022 in the killing of Ms. Smart.

Ms. Smart’s body has never been located, and her family declared her legally dead in 2002. But they are still seeking closure and remain determined to find her body, said Sheriff Ian Parkinson of San Luis Obispo County.

For decades, the case has been one of California’s most haunting mysteries. Many residents still recall seeing billboards and news coverage of the young college student after she went missing. In more recent years, the case was taken up by true crime podcasts, including “Your Own Backyard,” which sifted through clues before the 2022 conviction and continues to investigate.

Mr. Parkinson said at a news conference on Friday that early testing of the soil found compounds that were consistent with decomposed human remains, though investigators had not found actual remains at the site. The evidence suggested that remains were either present or had once been present at the property. Investigators have not linked the compounds to any specific person.

“So we can’t call it Kristin, but we think there’s evidence to support human remains,” Mr. Parkinson said at a Friday morning news conference.

Investigators on Friday were still searching the property, and the sheriff said they were prepared to go as long as it takes until “we either find Kristin” or were satisfied that they had thoroughly searched everything.

Mr. Flores, 49, remains in prison serving a sentence of 25 years to life, after he was found guilty of first-degree murder in Ms. Smart’s death in 2022.

Prosecutors said that Mr. Flores, who was a fellow student at California Polytechnic State University, San Luis Obispo, sexually assaulted Ms. Smart and killed her after an off-campus party on May 25, 1996. The disappearance of Ms. Smart, a college freshman, set off an extensive search and captured national attention at the time.

The authorities had identified Mr. Flores as a person of interest early in the investigation, but it took nearly 25 years for them to gather enough evidence to arrest him.

He was charged with her murder in 2021 and convicted by a jury in Monterey County Superior Court, a neighboring jurisdiction where the case had been moved.

The authorities also charged Mr. Flores’s father, Ruben Flores, with being an accessory and alleged that he had helped his son conceal Ms. Smart’s remains. Mr. Flores was found not guilty.

Mr. Parkinson said that Ms. Flores had long been a person of interest, but she was not under any travel restrictions as part of the search warrant. She was, however, required to leave her residence during the search. She did not respond to a phone call on Friday.

Kirsten Noyes contributed research.