Police said that thieves in California stole jewelry and gemstones worth millions of dollars after breaking into an unsecured security car returning from a jewelry show.

Authorities reported on Monday that the robbery occurred last week at a rural rest stop in southern California after the vehicle's two armed guards walked away.

The tractor-trailer, owned by the security corporation Brinks, had traveled overnight from a jewelry show in the San Francisco Bay Area to another event in the Los Angeles area. According to Los Angeles sheriff's sergeant Michael Mileski, it was not immediately clear if the suspects followed the vehicle during its 375-mile (604-kilometer) journey or stumbled upon it at a rest break and committed a crime of opportunity.

Mileski stated that the guards reported the theft at 2 a.m. on 11 July after discovering that the trailer's lock had been tampered with. Investigators are attempting to discover how the lock was compromised.

It was unclear how long the guards had left the vehicle unattended at the Flying J gas station and truck stop in the unincorporated community of Lebec, some 75 miles (121 kilometers) north of Los Angeles.

Brandy Swanson, the group's director, stated that the stuff was placed onto the truck late on 10 July, following an exhibition organized by the International Gem and Jewelry Show in San Mateo, south of San Francisco. She stated it was destined for an event in the Pasadena convention center just north of Los Angeles.

While Swanson stated that 18 victims reported losses over $100 million, Brinks noted that the stolen items were worth less than $10 million.

Brinks stated that, according to the information provided by clients before shipping their belongings, the total worth of the missing items is less than $10 million. According to the provisions of our contract, we will ultimately reimburse our customers for the value of their stolen property while cooperating with law enforcement.

Monday afternoon, neither Brinks nor the International Gem and Jewelry Show responded promptly to calls for comment.

Swanson stated that sellers who travel between jewelry exhibitions frequently underinsure their items due to financial constraints.

"This is where the disparity arises. These are mom-and-pop businesses, said Swanson. "They are heartbroken, and some of these individuals have lost their entire means of subsistence."

Based on the insurance, Mileski stated that detectives estimate the theft at $10 million, but they expect the amount to rise. Investigators are examining surveillance footage from local businesses to determine if the crime was captured on camera. According to the sergeant, many suspects are thought to have carried out the robbery.