Gardner Museum Heist Video Released 25 Years On

The FBI has released grainy surveillance video from 25 years ago showing an unauthorised visitor entering a Boston museum the night before it was robbed.

Authorities hope the six-minute, low-resolution video will spark leads to help recover the 13 pieces of stolen artwork, worth at least $500m.

The robbery at the Isabella Stewart Gardner Museum was one of the largest such heists in US history.

It took place in the early morning hours of 18 March 1990, after two men dressed as police officers were admitted by a security guard to the museum.

They told the security guard that they were responding to a report of a disturbance within the compound and were let in "against museum policy", according to a statement by the FBI.

The guard were apparently overpowered and found duct-taped to chairs in the museum's basement the following morning.

The culprits were never found, and the guard who let them in has long denied any involvement in the robbery.

The new footage, captured by museum CCTV, shows a security guard appearing to hit an intercom button to grant access to a man who can be seen in the museum's reception area at about 12:49 am on 17 March 1990 - almost exactly 24 hours before the heist.

The man is also seen getting out of a car matching the general description of one reported to be parked outside the museum minutes before the theft.

He uses the same rear entrance as the thieves, according to the office of US Attorney Carmen Ortiz, which released the video.

The similarity of events seen in the video and what happened on the night of the robbery has led to speculation a dry run for the actual heist took place the previous night.

Ms Ortiz said, however, that "we don't have any specific information that that's what happened".

The guard who buzzed the thieves in on the night of the robbery, Richard Abath, was a 23-year-old rock musician moonlighting as a security guard.

In the new video, officials do not identify the guard but The Boston Globe and The New York Times said the guard seen in the footage was indeed Mr Abath.

The statute of limitations on the crime has long passed, meaning that if the thieves are found they will not face prosecution.

But authorities hope to recover the art and the museum has offered a $5m reward for information that leads to the recovery of the stolen artwork in good condition.

Among the stolen works were pieces by Rembrandt, Monet and Vermeer. The museum features the collection of Ms Gardner, an eccentric Boston socialite who died in 1924.