Federal authorities announced charges against a ring of nine people for thefts of millions of dollars worth of paintings, sports memorabilia and other valuables including World Series rings belonging to baseball legend Yogi Berra and an MVP trophy awarded to New York Yankees teammate Roger Maris.

The thefts took place over more than two decades at 20 different museums and institutions across Pennsylvania, New Jersey, New York and North Dakota, the U.S. Attorney for the Middle District of Pennsylvania said Thursday.

Investigators believe some of the sports memorabilia had been melted down, including nine of Berra's 10 World Series rings, U.S. Attorney Gerard M. Karam said at a news conference.

The theft ring also allegedly stole an Andy Warhol silkscreen, a Jackson Pollock painting and the Hickok Belt awarded to Maris in 1961, when he set Major League Baseball's single-season record with 61 home runs. The Hickok Belt was given to the top athlete in the United States from 1950 to 1976.

It is unclear which items would be returned to their owners or to the museums, but authorities said some of those valuables had been recovered.

Eight of the nine people named as part of the theft ring have turned themselves in, Karam said. At least five had already entered into preliminary plea agreements on charges including theft of major artwork and conspiracy to dispose of major objects of cultural heritage, according to court records. The suspects are in their late 40s to early 50s and are Pennsylvania residents.

Karam said the ninth suspect, Nicholas Dombek, 53, is considered a fugitive.

The indictments allege the thieves transported the memorabilia and valuables and would melt the gold items down into transportable discs that were sold for hundreds of thousands of dollars -- but for way less than many of the items were worth.

Court documents also allege that Dombeck destroyed a painting by Jasper Cropsey by burning it, to avoid the stolen artwork titled "Upper Hudson" from being used as evidence against him.

Some of the thefts happened nearly 20 years ago including the 2005 theft from the Everhart Museum in Scranton, where the thieves shattered a glass door in the back of the building. They stole a 1949 oil-on-canvas painting by Pollock, "Springs Winter," then worth an estimated $11.6 million and a silkscreen by Warhol titled "Le Grande Passion," then worth an estimated $15,000.

Information from The Associated Press was used in this report.