Washington (CNN) -- Johnny Bench, Tony LaRussa and Steve Carlton, their 1980s-style hair shoved under their caps, look forever young in a substantial baseball card collection that's missing an owner.

Since June 24, the Metropolitan Police Department has been trying to find the rightful owner of well more than 500 cards, each carefully placed in a plastic protective sleeve.

A visitor to East Potomac Park found the cache of cards in a grassy area and notified police, who combed through crime reports but have thus far struck out on identifying the owner.

"We don't know if it fell off the back of a car," Lt. Nicholas Breul said Wednesday, indicating it's his guess that they were stolen.

Police publicized the find Wednesday and included photos of some of the collection. They aren't releasing all the information because they want to be sure whoever comes forward can provide extensive details before they turn them over.

The Topps and Fleer cards are of Major League Baseball players from the 1980s and 1990s. Players include Reggie Smith, Gary Carter and Toby Harrah.

Breul won't hazard a guess on their value, but he indicated some might be worth about $1.

Of course, a few could be worth more. If no one successfully claims them, the cards may be auctioned and serious collectors would get a better handle on their worth.

"So much depends on condition," Breul told CNN.

The department spokesman said he's not an avid baseball fan. After all, he grew up in Washington, which twice lost the Senators to other cities and whose Nationals have been dependable cellar-dwellers.

He is friends with Boston Red Sox fans and has at least one connection with one of the finds.

"That Fred Lynn card is pretty cool," Breul said, referring to the outfielder who starred for the Sox in the '70s.

Anyone with information or believes the set is theirs can contact the department's Public Information Office at (202) 727-4383 between 7 a.m. and 11 p.m. ET Monday through Friday.

CNN's Phil Gast contributed to this report.