US police have said a podcaster’s efforts have helped them track down a suspect in the killing of California college student Kristin Smart nearly 25 years ago.

Chris Lambert detoured from his musical career three years ago to create a podcast about Ms Smart’s disappearance in 1996, when she was aged 19.

San Luis Obispo County Sheriff Ian Parkinson said Mr Lambert’s efforts helped bring forward witnesses that led this week to the arrest of Paul Flores and his father Ruben, who have appeared in court over the disappearance.

Kristin Smart
Kristin Smart (FBI/AP)

Mr Lambert said he never expected the results he achieved. Meanwhile, his podcast, Your Own Backyard, hit 7.5 million downloads on Thursday. It was the number two podcast on iTunes.

He said a billboard on the side of the road on California’s Central Coast led him on a detour three years ago from his career as a singer-songwriter and recording engineer.

The 33-year-old says the podcast has taken over his life, saying: “I can’t step away from it for more than a few days.

“I just get sucked right back in because I want to be resolving things.”

It was an unlikely turn for someone who refers to himself as a shy, “random boy with a beard”, and it has produced results he never imagined.

Paul Flores
Paul Flores was arrested this week over Ms Smart’s murder (San Luis Obispo County Sheriff’s Office/AP)

On Tuesday, as San Luis Obispo County Sheriff Ian Parkinson announced the arrests, he credited Mr Lambert with helping draw worldwide attention to the case and bringing forward several key witnesses.

Flores, a long-time suspect in the case, and Ms Smart were fellow first-year students at the California Polytechnic State University campus in San Luis Obispo.

Now 44, Flores has been charged with murdering the 19-year-old while trying to rape her in his dorm room, prosecutors said.

His father, Ruben Flores, 80, was charged as an accessory after authorities said he helped hide Ms Smart’s body, which has never been located.

Paul Flores’ lawyer has declined to comment on the criminal charge. A lawyer for Ruben Flores said his client is innocent.

Police digging in a back yard
Police dig in an area in the back yard of the home of Ruben Flores, in Arroyo Grande, California (AP)

Despite the podcast’s success, all the attention is not leading to any money for Mr Lambert – he takes no advertising for the broadcast, relying instead on donations.

His is the latest in a line of true-crime podcasts to play a role in an arrest, a court appeal or even an exoneration.

Up And Vanished led a man confessing to the killing of a Georgia beauty queen, while Serial helped a convicted murderer win a new trial in Maryland.

In The Dark unearthed new evidence in a case prosecutors dropped, instead of seeking a seventh trial against a Mississippi man who spent decades on death row.

Mr Lambert was just eight when Ms Smart vanished a short drive up the coast from his own home in the small town of Orcutt, about 140 miles north-west of Los Angeles.

Ruben Flores
Paul Flores’ father Ruben was arrested in connection with the case (San Luis Obispo County Sheriff’s Office/AP)

It scared him that someone had gone missing, and no-one knew what happened.

For more than two decades, a billboard featuring a photo of a grinning Ms Smart advertised a 75,000 dollar (£54,000) reward for information over the case. It is located in the town of Arroyo Grande, where Paul Flores grew up and where his parents still live.

Mr Lambert passed the billboard many times, and it ultimately motivated him to start investigating.

“I thought I’d give it a shot and see if I could get a few people talking,” he said.

“All I have to do is get over my shyness and start calling these people out of the blue and start asking really personal questions.”

He bought some high-quality recording equipment and began making calls. He located overlooked or reluctant witnesses who had not spoken with police, he said.

People opened up to Mr Lambert and he encouraged them to contact investigators with relevant information. Then, deputies started calling him to connect them with the people he interviewed.

“What Chris did with the podcast was put it out nationally to bring in new information,” Sheriff Parkinson said.

Chris Lambert
Mr Lambert records the arraignment of Paul Flores, and his father Ruben Flores, at the San Luis Obispo Superior Court in California (AP)

“It did produce some information that I believe was valuable.”

A former colleague of Paul Flores’ mother, Susan Flores, told him Mrs Flores came into work after Memorial Day weekend 1996 – when Ms Smart went missing – saying she did not sleep well because her husband had gotten a phone call in the middle of the night and left in his car.

“The speculation has been all along that Paul (Flores) called his dad in the middle of the night and his dad came up and helped him get rid of Kristin’s body,” Mr Lambert said.

A tenant who lived for a year at Susan Flores’ home also told him she heard a watch alarm go off every morning at 4.20am. Ms Smart had worked as a lifeguard at 5am at the Cal Poly pool, so it is possible she set her watch to wake her up at that early hour.

“That seems to be the moment in the podcast series that most people have been just completely shaken,” Mr Lambert said.

“This may be the piece of evidence that points to the fact that Kristin was buried in that backyard or that her belongings were buried in that backyard.”

Susan Flores told KSBY-TV in March in the only interview she has granted that she could “shoot a lot of holes into a lot of (Mr Lambert’s) lies”.

Chris Lambert
Mr Lambert works as a musician and recording engineer (AP)

She said Mr Lambert never contacted her. He said he sent an intermediary to her house, and Susan Flores threatened to call the police.

The podcaster’s efforts to speak with Paul Flores were also fruitless, he said.

Mr Lambert spoke with a former Australian exchange student at Cal Poly who said he saw Flores and Ms Smart struggling near where the missing teenager was last seen.

Mr Lambert said investigators had dismissed that account in the early years of the probe.

He has developed a close relationship with the Smart family, who issued a statement after the arrest, praising his skills and “unselfish dedication”.

Mr Lambert wrote on Instagram: “For most of my life, Kristin Smart has been a face on a billboard.

“I’ve learned about Kristin the daughter, Kristin the big sister, Kristin the friend, the neighbour, the roommate. Kristin the swimmer. Kristin the dreamer. And I’ve learned that you can miss a person you never even got to meet.”