Federal authorities say they arrested nine people connected to a string of artwork and sports memorabilia thefts over the last 20 years – including World Series rings belonging to Yankees legend Yogi Berra.

The group is accused of stealing nine World Series rings, seven other championship rings and two MVP plaques awarded to Berra. These items were stolen from the Yogi Berra Museum and Learning Center in Little Falls, New Jersey, in 2014. Officials say these items are worth more than $1 million. None of the items have been recovered.

“My family is grateful that those responsible for the theft have been apprehended, and deeply saddened that none of those pieces of sports history will be recovered,” Lindsay Berra, granddaughter of Yogi Berra, wrote in a statement.

Lindsay Berra is a member of the museum’s Board of Trustees.

“I remember when my grandfather first heard about the robbery, his main concern was that the Museum was still safe for kids to come and visit. Educating the next generation was always his priority for the Museum,” she said.

The group is accused of stealing from 20 different museums in New Jersey, New York, Pennsylvania and North Dakota.

Other stolen items include six championship belts stolen in 2015 from the International Boxing Hall of Fame in Canastota, New York; five trophies worth over $400,000, including the 1903 Belmont Stakes Trophy, stolen in 2013 from the National Racing Museum & Hall of Fame in Saratoga Springs, New York; and the painting "La Grande Passion" by Andy Warhol stolen in 2005 from the Everhart Museum in Scranton, Pennsylvania.

Officials say that the group melted the memorabilia down “into easily transportable metal discs or bars. The conspirators sold the raw metal to other individuals in the New York City area for hundreds or thousands of dollars, but significantly less than the stolen items would be worth at fair market value.”