The New York City Police Department expanded its search yesterday for Clark Rockefeller, who allegedly kidnapped his daughter during a supervised custodial visit in Boston on Sunday.

Law enforcement authorities said they searched marinas on City Island and the West Side, and Boston police said they found one of two vehicles Mr. Rockefeller had traveled in and were questioning its owner yesterday.

Mr. Rockefeller, who Boston police say is 48, seized his 7-year-old daughter, Reigh, during a supervised custodial visit Sunday and then fled to New York City, according to law enforcement authorities. Police said Mr. Rockefeller was trying to reach his yacht, Serenity, on Long Island with his daughter.

The NYPD said Monday that it believes Mr. Rockefeller is a descendant of Nelson Rockefeller, but a spokesman for the family of John D. Rockefeller Sr., Fraser Seitel, said the alleged kidnapper has no relationship to the family. (Nelson Rockefeller, a former vice president, was a son of John D. Rockefeller Jr.)

“It’s a very famous name, and it’s a name that is connected to wealth, and credibility, and decency, and philanthropy. So if you had to take another name, it’s a good one,” Mr. Seitel said.

A senior archivist at the Rockefeller Archive Center, Amy Fitch, said Clark Rockefeller is not a descendant of William Avery Rockefeller, the father of John D. Rockefeller Sr. and William Rockefeller.

Mr. Rockefeller’s true identity is a mystery. Boston police have said he has used a number of aliases throughout his life, including James Frederick, Michael Brown, and J.P. Clark Rockefeller. Some acquaintances of Mr. Rockefeller believed he was a physicist, some a mathematician, and others were told he was involved in the financial industry, the Associated Press reported.