'Free Luigi Mangione' billboard seen from Southern California freeway

LOS ANGELES - While New York detectives say they have plenty of evidence to prove 26-year-old Luigi Mangione committed the murder of UnitedHealthCare CEO Brian Thompson, supporters of the Ivy League graduate insist he's being framed.

Mangione has risen to "superstar status" since his arrest Monday at a McDonald's in Altoona, Pennsylvania, located about 230 miles west of New York City, with many idealizing the defendant for what some call "vigilante justice" over health care policies, corporate practices and economic frustrations.

SUGGESTED: 'Hero' Luigi Mangione supporters insist he's being framed

On Thursday, a billboard in support of Mangione was spotted off  the southbound 215 Freeway at La Cadena Drive, entering Riverside.

"FREE LUIGI MANGIONE HE'S A HERO," is written in black in all capital letters against a pink background. 

It's unknown who put up the billboard. 

Mangione remains jailed without bail in Pennsylvania. His lawyer there, Thomas Dickey, has said Mangione intends to plead not guilty. Dickey also said he has yet to see evidence decisively linking his client to the crime.

Mangione’s arrest came five days after the caught-on-camera killing of Thompson outside a Manhattan hotel.

SUGGESTED: Vigilante justice? Murder of United HealthCare CEO provokes split emotions

Police say the shooter waited outside the hotel, where the health insurer was holding its investor conference, early on the morning of Dec. 4. He approached Thompson from behind and shot him before fleeing on a bicycle through Central Park.

Mangione is fighting attempts to extradite him back to New York so that he can face a murder charge in Thompson’s killing. A hearing has been scheduled for Dec. 30.