This is a Robbery: The World's Biggest Art Heist

A museum guard buzzes in two men dressed as cops, who vanish 81 minutes later with a priceless Rembrandt and a dozen other works of art.

Was the heist an inside job? As law enforcement scrutinizes the museum's security measures, a suspect emerges, but missteps hinder the investigation.

Amid apparent sightings of the stolen art, criminal activity connected to organized crime leads to possible perpetrators and a motive for the robbery.

An informant and a sting operation open up new avenues in the investigation, which federal agents follow to the home of a small-time mobster.