"That does beg the question, 'When will we get hit again?'" he said.
While looking into the robberies, detectives noticed a similar pattern.
In most cases, two to eight men in their late teens to mid-20s entered the jewelry stores during normal business hours, smashed the cases with hammers or other tools and stole jewelry, police said.
The incidents typically lasted just 30 seconds before the men fled in waiting vehicles that were double parked near the store, police said.
The suspects often wore gloves, some wore masks, others hats and hooded sweatshirts, police said.
In some robberies, police said they discovered that women who were likely working with the robbers had visited the stores several days beforehand to check out the jewelry and security measures.
All robberies appeared to be sophisticated and well-organized, police said.
Pasadena police arrested four men in connection with a Nov. 17 smash-and-grab robbery at the Pasadena Jewelry Mart after they attempted to flee from the scene.
Lorenz said the Glendale and Pasadena robbery suspects were not connected.
Glendale police had arrested three people in connection with the theft following a freeway pursuit after the robbery. But detectives haven't connected them to the robbery, Lorenz said.
Police will continue to look for six suspects in the Glendale robbery. They were described as black and wore dark-colored hooded-sweatshirts. The suspects fled in a dark-colored Dodge Charger with no license plates and a red Buick Regal.
Jewelry store owners should immediately notify police if a large group enters their businesses or if someone appears to be suspicious, Lorenz said.
"Let us determine whether it is good or bad," he said.
Most of the jewelry stores that were robbed used tempered glass, which police said helped prevent or lessen the total loss.
Police urged jewelry store owners to make sure surveillance equipment is working properly to help identify thieves.
Executive Jewelers Owner Garo Anserlian said the recent robberies have prompted him to be more suspicious of people who enter his Montrose store.
To avoid being robbed, Anserlian said he always makes sure that at least two employees are in the store, and that his security cameras are working.
"Of course, we are concerned," he said. "We are trying to be more careful."
Anyone with details about the robbery is urged to call Glendale police at (818) 548-3987, or Glendale Crime Stoppers at (818) 507-7867. To remain anonymous, call the Los Angeles Regional Crime Stoppers' tip line at (800) 222-TIPS.