BETHESDA, Md. — Like many people excited about a new home, Lamont Butler invited friends over to check his out. He had a lot to show them. The Bethesda mansion, among the largest in the region, featured floors of imported marble, 12 bedroom suites, six kitchens and a history of playing host to political gatherings, including ones during which Bill Clinton and Al Gore helped plant trees out back.

But the personable 28-year-old didn’t own the mansion; he had simply slipped inside and claimed it. Taking part in an odd and perplexing phenomenon popping up in cities across the country, Butler said the Bethesda mansion belonged to him because he is a Moorish American National. He’d drawn up paperwork that he said proved it all, with references to a 1787 peace treaty and the Vienna Convention on Consular Relations.

Montgomery County police call Butler’s stay in the mansion, which lasted only a few hours, something entirely different from a legitimate claim: breaking and entering, fraud and attempted theft. They say it is one of the most audacious local cases in what law enforcement officers called a growing national trend where self-described “sovereign” nationals try to move into homes they don’t own.

This month in Memphis, a woman saying she was a Moorish American was evicted after a SWAT team moved in on a 9,000-square-foot mansion she said she owned. Tabitha Gentry was charged with trespassing and burglary, but in court she denied the legitimacy of the charges, repeatedly interrupted the judge and invoked her sovereign rights.

Similar cases have occurred around the nation, where sovereign nationals have slipped into empty houses, sometimes going unnoticed for a week or two, authorities say.

“It’s going on in every state,” said Kory Flowers, an investigator with the Greensboro, N.C., police and a national expert on sovereign groups.

Police in the Washington area say they haven’t seen nearly as many sovereign cases as other states, notably California, North Carolina and Georgia. In terms of the property’s value, the Bethesda mansion incident appears to be unprecedented in the area.

Moorish American sovereigns get their name in part from the Moorish Science Temple of America, a religion formed in the early 20th century that preached obeying laws and had an uplifting message for African Americans: Be proud of who you are, said Spencer Dew, an expert on Moors and professor of religious studies at Centenary College of Louisiana.

But in the years since, a series of Moorish offshoots have twisted some tenets for their own gain – notably the idea that black people lived in what is now the United States long before the arrival of Europeans, Dew said.

Sovereign nationals, law enforcement officials say, use that tenet to justify the assertion that land instruments such as mortgages are not valid and that local laws do not have to be obeyed.

Moving into foreclosed or unoccupied houses is one of the more visible ways sovereign nationals break the law. The gambits are rarely successful, often ending within hours or days when neighbors call the police after noticing unusual activity in the large residences sometimes targeted.

Sovereigns break other laws, too. They sometimes don’t register their cars with state motor vehicles officials, driving around instead with self-styled license tags. And they cause headaches for those who investigate them, targeting officials for retaliation by filing million-dollar liens on their properties. Police officers, judges and other public officials have had to take time off work or turn to lawyers to untangle their land records, several public officials said.