The United States is likely to wait a while before lodging a formal request for the extradition of a Japanese researcher accused of stealing genetic materials on Alzheimer's disease from a U.S. research lab and sending them to Japan, a U.S. federal prosecutor said Thursday. Washington is continuing unofficial negotiations with Tokyo over the proposed extradition of Takashi Okamoto, the prosecutor told reporters after a preparatory hearing at a federal court in Akron, Ohio.

The hearing was held to consider the case of Okamoto's alleged accomplice, Hiroaki Serizawa, an assistant professor of molecular biology at the University of Kansas.

The trial of Serizawa, who has pleaded not guilty, is scheduled to begin Nov. 5.

Federal prosecutors in Ohio indicted Okamoto and Serizawa in May on charges of stealing genetic materials developed by the federally funded Cleveland Clinic.

Okamoto resigned from his research position at the clinic in July 1999. He was then employed by the government-funded Institute of Physical and Chemical Research (Riken) in Japan but resigned in late July.