It had the potential to be a breakthrough in the 25-year investigation into the Isabella Stewart Gardner Museum heist. The six minutes of surveillance footage showing a shadowy figure entering the museum after midnight — exactly 24 hours before thieves made off with $500 million in artwork — generated tips from former museum employees, Internet sleuths, even car enthusiasts who thought they could identify the vehicle seen in the clip.
A Quincy lawyer said his client was convinced the man in the video was an old associate in the antiques business — so sure that the client was afraid “of being killed” if he dared to publicly identify the man. A California woman who once worked as a guard at the Gardner is sure the man in the video was her supervisor, a belief later shared by three of her old colleagues.
Now, three months after the footage was released, investigators said they still haven’t identified the man who entered the side door of the museum early March 17, 1990, leaving them unable to answer a critical question: What was he doing there, in violation of security protocol, the night before two robbers posing as police officers conned their way into the same door and made off with 13 works of art, including a Vermeer and three Rembrandts?
Christina Diorio-Sterling, a spokeswoman for the US attorney’s office, said the investigation into the Gardner robbery and the recently released video “is very much active and ongoing,” though she would not discuss specifics of the case.
“Since the release of the video, we have received many tips and information that continue to be vetted,” she said. “We will continue to use all resources at our disposal, including enlisting the public’s help, to solve this crime.”
Though it has been discounted by investigators, one of the more promising possibilities put forward is that the man in the footage was Lawrence P. O’Brien, then the museum’s deputy security supervisor, who died in 2014 at age 77. Four former guards told the Globe they are convinced it is he, including one who has a “vague memory” of O’Brien returning once after museum hours to retrieve a wallet he had left at work.
“I know that’s Larry. He was stocky, and walked like that, always with his jacket collar up,” said another former guard, Cynthia Dieges, now a chef in Atlanta who worked as a manager in the museum’s security department between 1987 and 1992.
The three other former guards who believe the man in the video is O’Brien are Marj Galas, who lives in Los Angeles; April Kelley, a high school English teacher in Central Massachusetts; and Michael Levin, a Framingham lawyer. The four said they had not been contacted by investigators, though Galas said she called an FBI hot line.
However, two former guards who knew O’Brien well told the Globe they do not believe the man in the video was O’Brien. His brother also disputes the ID.
“Larry’s hair was shorter than the fellow shown there,” said David O’Brien, 81, of Somerville.
The conflicting identifications are part of a frustrating attempt to solve the world’s greatest unsolved art heist, and they illustrate the difficulties investigators have faced as new evidence emerges amid old theories of the crime.
The dark figure, who stands by the watch desk for several minutes, is difficult to see in the grainy footage. He also stays out of the view of the museum’s surveillance camera for most of the time, though he appears at one point to be fumbling through paperwork or with some other object.
The old security footage was apparently overlooked and mixed in with other evidence collected at the beginning of the case. In the last year, a team of new investigators began reviewing the old evidence and discovered the video, which apparently had not been viewed before. Authorities released the video to the public in hopes that someone might know the unidentified man and what he was doing at the Gardner after hours. Was it an innocent visit? A dry-run the day before the heist?
One of the only people who might be able to answer those questions is Richard Abath, the then-23-year-old guard who let the shadowy figure into the museum that night. He is also the same guard who was tied up by the robbers after he let them into the same door the following night.
Twenty minutes before the robbers arrived, at about 1 a.m. on March 18, Abath opened the side door of the museum in what several security officials have told investigators was a violation of museum rules.
Abath had told investigators he often opened the side door during his rounds: in fact, he had done it the night before. But he never told investigators he had let someone inside.
Abath has recently told investigators that he could not identify the man in the video and that he could not recall the visit at all. He has declined to answer reporters’ questions about the video.
It could be easy to discount O’Brien as the man in the video based on the memories of his brother and two former coworkers, one of whom was his supervisor. O’Brien, who was 53 at the time of the heist and had been interviewed about it before his death, also never said anything about being at the museum the night before.
But the four former coworkers maintain it is he.
A Globe review of state records shows that at the time of the heist, O’Brien owned a 1982 Ford Escort, one of the types of cars that enthusiasts have told investigators could be the one seen in the surveillance footage.
But officials don’t seem persuaded.
Kristen Setera, a spokeswoman for the FBI, said the agency “has followed up on all leads, including the one involving Mr. O’Brien.” She said she could not elaborate on the investigation.
Diorio-Sterling said in a statement that “the public should be assured that we pursue all credible leads.”
Shelley Murphy of the Globe staff contributed to this report. Milton J. Valencia can be reached at email@example.com. Follow him on Twitter @miltonvalencia. Stephen Kurkjian can be reached at Stephenkurkjian@gmail.com.