A former security guard has told investigators that he doesn’t remember letting a man into the Isabella Stewart Gardner Museum the night before it was robbed of $500 million worth of artwork in 1990 and can’t identify him from a video, according to several people familiar with the probe.
Federal investigators showed the former guard, Richard Abath, a surveillance video that depicts him letting an unidentified man into the museum at 12:49 a.m. on St. Patrick’s Day 1990 in an apparent violation of security protocol.
The man, who stands by the watch desk for several minutes, remains out of view of the museum’s surveillance camera for most of the time and appears to be fumbling through paperwork, or possibly showing something to the then-23-year-old guard.
Yet, when confronted by authorities recently about the decades-old evidence, Abath, who lives in Brattleboro, Vt., said he didn’t recognize the man and had no recollection of the encounter, according to those familiar with the investigation.
Abath could not be reached for comment.
The FBI and US Attorney Carmen Ortiz declined to comment on Abath, citing the ongoing investigation into the world’s largest art heist and Boston’s most enduring mystery.
Law enforcement officials said the video raises questions about whether the man was conducting a dry run for the robbery, which occurred just over 24 hours later.
At 1:24 a.m. on March 18, 1990, two thieves dressed as police officers banged on the same side door, claiming to be investigating a disturbance, and were buzzed inside by Abath. They tied up Abath and the other guard on duty and vanished with 13 masterworks, including paintings by Rembrandt, Vermeer, Manet, and Flinck.
The thieves took the museum’s surveillance video from the day of the heist, but not from the night before. That footage was collected by the FBI during the early days of the investigation. Ortiz said a team of investigators reviewed the original evidence and one of them, Assistant US Attorney Robert Fisher, requested the video.
Tips have been flowing in to the FBI and the Gardner Museum since authorities released the grainy, black-and-white video Thursday, seeking the public’s help in identifying the unknown man.
Anthony Amore, the museum’s security director, said that as of Friday afternoon he had received more than a dozen tips “from all over the place” and is hopeful investigators will be able to identify the mystery man.
“I’m always optimistic,” said Amore, who has partnered with the FBI and federal prosecutors to investigate the heist for the past decade.
The FBI also received a handful of tips after the video’s release, according to Kristen Setera, a spokeswoman for the FBI.
Two years ago, the FBI announced it was confident that it had identified the thieves, but declined to name them, citing the ongoing investigation. Authorities said they believed some of the artwork changed hands through organized crime circles, and moved from Boston to Connecticut and Philadelphia, where the trail went cold. They also said they believed the thieves died shortly after the heist, leaving the fate of the artwork unknown.
Setera said the FBI continues to believe “with a high degree of confidence that we know the identities of these individuals and these individuals to whom we are referring are deceased.”
An FBI PowerPoint presentation that offers its theory of the case suggests that a number of suspects were involved in the heist, most of whom are dead. They include George Reissfelder, of Quincy, who died of a cocaine overdose in 1991 at age 51; and Leonard V. DiMuzio, of Rockland, who was 42 at the time of the heist and was found shot to death in East Boston in 1991.
In the past few years, the FBI has focused on Robert Gentile, an aging Connecticut mobster who was arrested earlier this year.
Gentile allegedly boasted to an undercover FBI agent that he had two of the stolen Gardner paintings and would sell them each for $500,000, according to federal prosecutors. Gentile, 79, of Manchester, Conn., has denied knowing anything about the whereabouts of the paintings.
Globe correspondent Sara DiNatale contributed to this report. Shelley Murphy can be reached at Shelley.Murphy@globe.com. Follow her on Twitter @shelleymurph.