BERLIN, Conn. — A Connecticut family is convinced that the mysterious man accused of kidnapping his daughter in Boston and wanted for questioning in the 1985 disappearance of a California couple was a German student who lived with the family decades ago.

Immigration officials confirmed yesterday they have joined the investigation into the background of Clark Rockefeller, who is jailed in Boston on charges he snatched his 7-year-old daughter, Reigh, last month in an elaborately planned kidnapping.

Steve Savio, 39, of Berlin, Conn., said yesterday he is “100 percent certain” that Rockefeller is the same person who boarded with his family in 1980 under the name Christian Gerhart Reiter at age 17. His mother and brother agree.

“The first pictures I saw of him when he didn’t have any glasses on, didn’t look anything like him,” Savio said in an interview yesterday with the Associated Press. “But the pictures after he was apprehended, with the glasses, those look just like him.”

Mr. Savio said Greenwich police interviewed his family in 1988 about a possible connection between Mr. Reiter and the disappearance of Jonathan and Linda Sohus, of San Marino, Calif. The FBI and German authorities interviewed them this week about Mr. Reiter and Mr. Rockefeller, he said.

Police have said Mr. Rockefeller, 48, snatched his daughter from a Boston street on July 27 in an elaborately planned kidnapping in which he hired two people to drive them to New York.

He was caught Saturday in Baltimore, where he had bought a home and boat. Prosecutors said 300 one-ounce gold coins and $12,000 in cash also were found in Mr. Rockefeller’s apartment following his arrest.

Authorities have said they have no record of Mr. Rockefeller before 1993, and he claims he has no memory of his life before then. He had refused to talk to investigators or reporters.