SAN LUIS OBISPO COUNTY, Calif. (KRON) – San Luis Obispo County District Attorney Dan Dow on Wednesday announced charges will be filed against Paul Flores and his father Ruben Flores for the 1996 homicide of Cal Poly student Kristin Smart.

Paul Flores, 44, has been charged with first-degree murder.

Paul Flores (left) and Ruben Flores (right) / San Luis Obispo County DA

In a press conference Wednesday, Dow said it is believed Paul Flores killed Smart during an attempted rape.

Ruben Flores, 80, is charged with accessory after the fact to the crime of murder. He is accused of helping hide Smart’s body after she was murdered.

“These charges mark a major milestone,” said Dow. “Today, we make the first move toward bringing justice to Kristin, her family, and the people of San Luis Obispo County.”

Paul Flores and Ruben Flores are scheduled to be arraigned April 15.

The son and father were arrested Tuesday.

San Luis Obispo County Sheriff Ian Parkinson said arrests came after a search of the elder Flores’ home last month using ground-penetrating radar and cadaver dogs turned up new evidence linked to Smart’s killing, though her body has not yet been located.

Smart, 19, of Stockton, was last seen May 25, 1996, while returning to her dorm at California Polytechnic State University campus in San Luis Obispo after an off-campus party.

he was inebriated at the time and Flores, a fellow freshman at the school, had offered to walk her home.

Flores killed Smart in his dorm room, Dow said.

Dow said in more recent years Flores frequented bars around his home in the Los Angeles area of San Pedro and may have committed other sexual assaults. He urged the public to come forward with any information.

A lawyer for Paul Flores has declined to comment. A lawyer for Ruben Flores said his client is innocent.

Paul Flores has been under suspicion almost from the start, but the case picked up steam in the past couple years after Parkinson ordered a thorough review of the evidence and a fulltime cold case detective was hired.

New witnesses came forward and warrants allowed investigators to intercept and monitor Paul Flores’ phone and text messages and search his own home, along with those of his mother, father and sister that turned up new evidence, Parkinson said. He declined to offer more details because search warrants are sealed.

Parkinson also credited the podcast “Your Own Backyard” for giving the case renewed widespread attention that led to a key witness coming forward.

The podcast’s creator, Chris Lambert, was a musician who grew up in the area and was intrigued by a billboard offering a $75,000 reward for information leading to Smart.

“Driving past that billboard was a periodic reminder that, oh yeah, they still haven’t found that girl,” Lambert said in a video posted on the podcast website. “It’s different when somebody goes missing in your own backyard.”

The Smart family filed a $40 million lawsuit in 1996 against Paul Flores and added the the university for allegedly not protecting their daughter. The case has been stayed awaiting a criminal case outcome, a family spokesman said.

They served over 40 search warrants at 16 locations over the years, collected nearly 200 new items of evidence and used modern DNA techniques to test more than three dozen older pieces of evidence. So much evidence was compiled that it would fill three terabytes on a computer hard drive, he said.

Ruben Flores was being held on $250,000 bail.

This is a developing story. Check back for updates.

The Associated Press contributed to this report.