A quarter of a century after a rookie security guard apparently let two thieves into the Isabella Stewart Gardner Museum by mistake, the largest unsolved art heist in history has made headlines again.

A just-released video raises new questions about the security guard, Richard Abath, who was 23 at the time. Abath violated policy on the night of the robbery by letting two thieves into the Boston museum, reports Edmund H. Mahoney for Hartford Courant. Both intruders were disguised as policemen.

Tim Murphy relates the story of the robbery for mental_floss: At 1:24 a.m. on March 18, 1990, the two imposters demanded entry to the museum. Abath let them in, only to be handcuffed and tied in the basement with another guard. The thieves then made off with 13 masterpieces worth an estimated $500 million, including paintings by Vermeer, Manet and Rembrandt, drawings by Degas and a Chinese beaker.

The new evidence is video from the night before the actual crime. It shows Abath on guard duty, opening the same door that he would open to the thieves and letting a man wearing a waist-length coat and upturned collar enter. Footage from an outside camera shows the man’s car, which matches the description of the vehicle reportedly parked outside the museum during the theft. On the first night, Abath opened the door at 12:49 a.m., nearly 24 hours before he did it again for the thieves.

Was it a rehearsal for the crime? The FBI, still investigating the case, just released the video to the public in the hopes that someone will recognize the man. However, the images are difficult to make out.​

Mahoney reports for the Courant that Abath never mentioned letting someone into the museum the night before. Security records show that the side door was opened, but it was attributed to Abath’s normal security rounds.

Officials haven’t explained why the video is only now coming to light, Tom Mashberg reports for the New York Times. The prosecutor, Robert Fisher, who took over the case about two years ago, apparently viewed it during a "complete re-examination of the case," U.S. Attorney Carmen M. Ortiz told The New York Times.

The museum has offered a $5 million reward for information that leads to the recovery of all stolen works in good condition.