Since it happened 30 years ago, the story of the Isabella Stewart Gardner Museum heist has been retold and analyzed over and over again. A new Netflix documentary, 'This Is a Robbery: The World’s Biggest Art Heist' looks at the famous 1990 crime with a new approach. Director Colin Barnicle joined Joe Mathieu on Morning Edition last week to discuss the project — and share his own theory on who might have done it.

Like many people who grew up in the Boston area, Barnicle and his brother Nick, an executive producer on the project, heard about the heist and were intrigued. Barnicle said they spent five years “obsessively” researching the robbery for the documentary in order to reenact the dramatic night of the crime.

“What we wanted to do was kind of grounded in more or less 'the night of' — have a good, accurate, intimate account of the robbery itself and branch out from there,” Barnicle said. They had to get creative to bring the story to the screen.

“Hypothetically, in any documentary you want to steer away from reenactments, but we didn't have anything,” Barnicle said. “There's no video, no arrests, there's no adjudication. It's a clean slate for this. Any reenactment you see in there [the documentary] is based on either a witness statement or a police report or an affidavit.”

WATCH: Barnicle talks to Joe Mathieu on reenacting history.

Art theft isn’t a run-of-the-mill robbery, and the film points out that the heist was likely done by a professional. Throughout his research, Barnicle found that the museum was a “known target” and considered an easy mark for criminals.

“The museum was operating on a budget loss. They didn't have a lot of money for security. It wasn't odd to find students as guards. But certainly they had been warned before,” Barnicle said, noting that the mafia had considered a theft. “Criminals are criminals; they are going to do stuff like this. And they were not art connoisseurs who went in there, but they were professional thieves.”

Despite millions of dollars in rewards, authorities never found the perpetrators. Barnicle came up with his own theory, but says we may never know the whole truth.

“It does look like there was a small crew who did this,” Barnicle said, noting that it has traces of organized crime. “Not immediately, but within 18 months after the crime, some of these participants start to drop dead fairly quickly and violently and they [took] their secrets to the grave with them.”

Because there was much less press coverage of the case in the early 90s, Barnicle said the art could have moved around unnoticed.

“In that period you could have had a Degas drawing handed to you, and thought it was a secondhand Degas, and swapped it at a swap meet,” Barnicle said.

FROM THE ARCHIVES: How GBH 2 covered the story on 1990.