A $5 million reward for masterworks stolen from the Isabella Stewart Gardner Museum a quarter century ago has failed to lead to their recovery, prompting authorities Tuesday to announce a new offer: $100,000 for the return of one of the least valuable items, a bronze eagle finial.

The reward far exceeds the value of the 10-inch-high gilded eagle, which was swiped from the top of a pole supporting a silk Napoleonic flag. It was taken along with 12 other pieces valued at $500 million, including masterpieces by Vermeer, Rembrandt, and Manet, in what remains the world’s largest art heist and one of Boston’s most baffling crime mysteries.