Investigators of a 20-year-old art heist at a Boston museum that was the largest such theft in history are stepping up their efforts.

Leaders of the Isabella Stewart Gardner museum say they're renewing their push to recover the works. They're seeking new DNA analysis and publicizing the museum's $5 million, no-questions-asked reward.

In the early hours of March, 18, 1990, two thieves walked into the museum disguised as Boston police. They bound two guards and took more than a dozen works of art including masterworks by Rembrandt, Vermeer, Degas and Manet.

They made off with more than a half-billion dollars in loot far too hot to sell. The mystery has never been solved.