LOS ANGELES -- Chris Lambert would like to get back to making music but he can't stop chasing a ghost that has haunted him for nearly 25 years.

A roadside billboard on California's Central Coast detoured him three years ago from his career as a singer-songwriter and recording engineer to create a podcast about the 1996 disappearance of college freshman Kristin Smart. It's taken over his life.

"I can't step away from it for more than a few days," Lambert said. "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.

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

The longtime suspect, Paul Flores, 44, was charged with murder in the killing of the 19-year-old while trying to rape her in his dorm room at California Polytechnic State University campus in San Luis Obispo, where both were freshmen, prosecutors said. Flores had been walking an intoxicated Smart home from a party and was the last person seen with her.

His father, Ruben Flores, 80, was charged as an accessory after authorities said he helped hide the 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.

Lambert has been thrust into the spotlight with the arrests. His eight-part series, "Your Own Backyard," hit 7.5 million downloads Thursday and it was the No. 2 podcast on iTunes. Lambert has been overwhelmed with messages from fans, tipsters and news reporters.

"It's driving me insane," he said, yet he remained focused, patient and polite during a 45-minute interview with The Associated Press on Wednesday.

All the attention isn't leading to a lot of money -- Lambert takes no advertising for the self-produced podcast, relying on donations.

His is the latest in a line of true-crime podcasts credited with producing results in court.

"Up and Vanished" led a man to confess to killing a Georgia beauty queen. "Serial" helped a convicted murderer initially win an order for a new trial in Maryland, though higher courts overruled that decision. "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.

Lambert, 33, was just 8 when Smart vanished a short drive up the coast from his home in the small town of Orcutt, about 140 miles (225 kilometres) northwest of Los Angeles. 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 Smart advertised a $75,000 reward. It's located near Flores' mother's house in the town of Arroyo Grande.

Lambert passed it 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," Lambert 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 hadn't spoken with police. He found others to recount what they told investigators, dug up old police reports, court files and news clippings.

People opened up to Lambert and he encouraged them to contact investigators with relevant information. Deputies started calling him to connect them with people he interviewed.

"What Chris did with the podcast was put it out nationally to bring in new information," Parkinson said without elaborating on the new evidence. "It did produce some information that I believe was valuable."

With a mix of interviews, a dramatic and eerie soundtrack Lambert created, and narration in his own warm voice that brims with conviction, the podcast drops compelling clues and reveals investigative missteps that impeded the case.

A former colleague of Paul Flores' mother, Susan Flores, told him Mrs. Flores came into work after Memorial Day weekend 1996 -- when Smart went missing -- saying she didn't 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 called his dad in the middle of the night and his dad came up and helped him get rid of Kristin's body," Lambert said.

A tenant who lived for a year at Susan Flores' home told him she heard a watch alarm every morning at 4:20 a.m. Smart had worked as a lifeguard at 5 a.m. at the Cal Poly pool, so it's possible she set her watch to wake up at that early hour.

"That seems to be the moment in the podcast series that most people have been just completely shaken," he 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, who hung up when called by the AP, told KSBY-TV in March in the only interview she's granted that she could "shoot a lot of holes into a lot of (Lambert's) lies."

She said Lambert never contacted her. He said he sent an intermediary to her house and Susan Flores threatened to call the police. His efforts to speak with Paul Flores were also fruitless, he said.

Lambert spoke with a former Australian exchange student at Cal Poly who said he saw Flores and Smart struggling near where Smart was last seen. Lambert said investigators had dismissed that account in the early years of the probe.

Lambert has developed a close relationship with the Smart family, who issued an effusive statement praising his skills and "unselfish dedication."

He is grateful to have grown close to the family. He feels like he's gotten to know Kristin Smart, but wishes he had the chance to meet her.

"For most of my life, Kristin Smart has been a face on a billboard," he wrote on Instagram. "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."

Correction:

This version corrects that the Maryland man ultimately did not get a new trial. Lower courts said he deserved a new trial but those decisions were overturned by a higher court.