The man last seen with Kristin Smart was convicted on Tuesday of killing the university student, who vanished from a California campus 25 years ago.
Jurors unanimously found Paul Flores guilty of first-degree murder, the San Luis Obispo Tribune reported.
His father, Ruben Flores, was charged as an accessory in another trial, where he was accused of helping to conceal the crime. A verdict was also expected in his trial.
Smart, 19, disappeared from California Polytechnic State University over the Memorial Day weekend in 1996. Her body was never found.
Paul Flores, now 45, was convicted of killing her during an attempted rape on May 25, 1996, in his dorm room at California Polytechnic, where both were first-year students.
He was the last person seen with Smart as he walked her home from an off-campus party.
His father, now 81, has been accused of helping to bury the student behind his home in the nearby community of Arroyo Grande, and later digging up the remains and moving them.
The son’s defence attorney, Robert Sanger, tried to pin the killing on Scott Peterson, who was later convicted of killing his pregnant wife and the foetus she was carrying.
Peterson was also a student at the university that year.
During his closing arguments, Mr Sanger told jurors that no attempted rape occurred.
He cast doubt on testimony from witnesses, including a student who was in Smart’s dorm who testified to seeing Flores in her room.
Mr Sanger also referred to forensic evidence offered by the prosecution as “junk science".
“This case was not prosecuted for all these years because there’s no evidence,” Mr Sanger said. “It’s sad Kristin Smart disappeared, and she may have gone out on her own, but who knows?”
Paul Flores had long been considered a suspect in the killing. He had a black eye when investigators interviewed him.
He told them he got it playing basketball with friends, who denied his account, according to court records. He later changed his story to say he bumped his head while working on his car.
But the father and son were only arrested in 2021 after the case was revived.
Investigators conducted dozens of fruitless searches for Smart’s body over two decades but in the past two years they turned their attention to Ruben Flores’s home, about 20 kilometres south of the university in the community of Arroyo Grande.
Behind latticework under the deck of his large house on a dead-end street, archaeologists working for police in March 2021 found a soil disturbance about the size of a casket and the presence of human blood, prosecutors said.
The blood was too degraded to extract a DNA sample.
The trial was held in Salinas, 177km north of San Luis Obispo, after a judge granted a defence request to move it.
The defence said it was unlikely that the Floreses could receive a fair trial with so much much notoriety in the city of about 47,000 people.
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Adnan Syed smiles and waves as he leaves the courthouse after a judge overturned his 2000 murder conviction and ordered a new trial in Baltimore, Maryland. Reuters -
Mr Syed's mother, Shamim Syed, hugs a supporter after her son was released. Reuters -
Erica Suter, director of the Innocence Project Clinic at the University of Baltimore School of Law and Mr Syed's lawyer, speaks outside the courthouse. AFP -
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Ms Mosby is embraced by a supporter after the judge overturned the murder conviction. Reuters -
Lawyer Chris Flohr embraces podcaster Sarah Koenig. Reuters -
Mr Syed was convicted of the 1999 murder of his ex-girlfriend Hae Min Lee. EPA -
Mr Syed is a free man after serving 20 years in prison. EPA -
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Supporters gather outside the Baltimore City Circuit Courthouse. Reuters -
Catina Carter wears a T-shirt reading '#FreeAdnan' outside the courthouse. Reuters -
Mr Syed spent 20 years behind bars for Lee's murder. AP
