(CBS) — Just a week before the 50th anniversary of the assassination of President John F. Kennedy, a historic fragment of that tragic event is the subject of a bitter lawsuit.

A Dallas man and his stepsister are suing the owner of a museum in the little Illinois town of Roscoe, near the Milwaukee border. As CBS 2’s Mike Parker explains, the nasty feud is over possession of the gravestone of JFK’s accused assassin.

President Kennedy’s presumed killer was assassinated himself and then buried during a small service in a Texas cemetery. Lee Harvey Oswald’s original gravestone is no longer there.

Today, it is inside a historical museum in Roscoe. Museum owner Wayne Lensing paid $45,000 for it.

“It is part of history, and that’s why it’s here,” Lensing says.

It’s in a Kennedy assassination exhibit, along with the hat and shoes of Oswald’s killer, Jack Ruby; a chunk of fence from the grassy knoll; and the actual Secret Service car that trailed JFK’s limo in Dallas.

It turns out that after the stone was vandalized, Oswald’s mother hid it inside a crawlspace in her house.

After her death, the new owners found it. Over decades, they began moving it to the homes of other family member for storage. One of the family members finally sold it to the Illinois museum out of her garage.

“Darn, it wasn’t much longer, next thing you know, now the other sides of the family — everybody’s squabbling,” Lensing says.

Now Dallas pub owner David Card says he and his step-sister, Cleo Lowe, are suing to get the marker back. They say they kept a photo of the slab and a list of assets they say proves they own it.

“This is the original tombstone of perhaps the most famous assassin in the history of the United States”, Card says.

Lensing says he feels like he is caught in the middle of a family dispute.

“It’s just costing me a lot of  money. Nobody wanted that stone,” he says.

Card counters: “The history was made here, for better or worse, and so the recognition of the history and the artifacts connected to it should be here as well.”

Lensing insists he bought and paid for the disputed gravestone and it will stay on display unless a Texas judge rules against him.

Either way, the rest of his extensive collections will be unaffected.

He is eager to get the dispute settled. He has spent more on legal fees than he did to purchase the headstone.

For more information on the museum, click here.

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