It happened last week between June 17 and June 18 at Huener Jewelry on Santa Monica Boulevard and Fairfax Avenue.
The owner's son told Eyewitness News the group took the store's entire inventory, including several safes.
"At first I thought they like cut a hole through the wall, and they got in, and they did a quick robbery and they left, but it turned out ... it took more than 24 hours," said Robert Goukasian, who told ABC7 the store's alarms never went off.
He said the four suspects completed the heist in two trips - one in the early morning hours and another late at night.
They broke in through the business next-door by cutting a hole through the wall and ultimately emptied two large safes that contained hundreds of pieces of one-of-a-kind jewelry.
In surveillance footage, you can see the four suspects working together to get into a safe. At one point, they're seen smiling, giving each other high-fives and even sharing hugs.
Detectives are now working to see if the group is connected to any other thefts.
The family has owned the jewelry store since 1986 and said despite the devastating loss, they aren't giving up.
"We've pretty much lost everything that we had in the store, but we are very optimistic. We are strong."
Anyone with information is urged to contact police.