The guard who let robbers into Boston\'s Isabella Stewart Gardner Museum 23 years ago is now under suspicion, officials said. Richard Abath let two thieves into the museum in March of 1990, The Boston Globe reported. The two thieves then stole 13 works of art valued at more than $500 million. Investigators believed Abath wasn\'t a part of the operation and made a mistake when he let the two men, who were dressed as police officers, into the museum, The Globe said. But now investigators are considering what role Abath played in the robbery after 23 years of pursuing dead ends, the newspaper said. The Globe said that Abath allegedly opened the door minutes before the robbers rang the buzzer, and allegedly may have been signaling them that he was ready for them. And motion detectors picked up only Abath\'s footsteps on the first floor gallery when one of the stolen paintings was taken, The Globe said. Abath is not being named as a suspect, and no one has ever been charged in the crime, The Globe reported.