A jewelry store in the Premium Outlets (formerly Paragon) in Livermore was robbed early Monday morning, police said.
They received a glass break alarm at 3:40 a.m. inside the Kay Jewelers at 2774 Paragon Outlets Drive.
The investigation led police to believe the suspects used a vehicle to drive through the front glass doors, according to reports.
The three suspects, who were wearing hoodies and masks, used sledgehammers to smash through the glass display cases containing jewelry, police said.
The three fled in two vehicles. One was described as a compact white station wagon and the other a white over tan sedan.
The outlets' on-duty private security did not hear anything unusual at the time but did see the vehicles drive out of the outlets at a high rate of speed, police said.
The loss has yet to be determined, police said.