Paul Flores, 44, was arrested at around 9:45 a.m. near Summerland Street and Western Avenue in Rancho Palos Verdes on suspicion of possessing a firearm as a felon, according to the Los Angeles Police Department.
In February and April of last year, deputies with the San Luis Obispo County Sheriff's Department served several search warrants in California and Washington in connection with the investigation, including at Flores' home.
Kristin Smart case: Search warrant again served at former classmate's home in San Pedro
Flores was the last person to be seen with 19-year-old Smart after the pair left a Cal Poly San Luis Obispo college party roughly 25 years ago.
Smart's body has never been found despite a two-decade search and sizable rewards seeking information.
September 2016: FBI renews search for Cal Poly San Luis Obispo student missing for 20 years
City News Service contributed to this report.