Chinese police have detained an American automotive engineer for more than a year on accusations he misused trade secrets _ the latest case of vague secrecy laws being used against an American in China.

Hu Zhicheng, a prize-winning designer of industrial catalysts to control auto emissions, has had letters from his family censored and has been denied reading materials during his detention in the port city of Tianjin, said the U.S. Embassy in Beijing. Last week police rejected an Old Testament he asked U.S. consular officers to bring him.

The stern treatment is being meted out in a business dispute over an automobile technology. Hu told U.S. officials that investigators have threatened him with multimillion-dollar fines unless he gives the rights to his U.S.-registered patent to a former business partner in Tianjin.

Hu's wife, a China-born naturalized American like her husband, said Tianjin authorities' real target is a China-based company she managed and whose cutting-edge products competed with those of the former business partner, the Hysci (Tianjin) Specialty Materials Co. Hysci, she said, complained that her startup was developing products unusually fast, prompting the trade secrets investigation.

"You don't sue someone just because you think their R&D is too fast," said Hong Li, who lives in the Los Angeles area with their two teenage children. "This case is being conducted illegally."

Police traveled from Tianjin to raid her company, seizing computer hard drives and production materials, Li said, declining to name the location of the company. The U.S. Embassy said prosecutors have twice sent the case back to police for further investigation _ often a sign the evidence is insufficient for an indictment.

Hysci declined comment, as did the Chinese company that employed Hu at the time of his detention. Prosecutors referred inquiries to the Tianjin police. The police information office said the criminal investigation is continuing but refused to elaborate other than to say "it is a complicated case."

A holder of nine patents in the U.S., Hu is just the kind of emigre Beijing has been eager to lure back to bolster an economy growing rapidly but short of talented managers and innovators. He has done research at the Massachusetts Institute of Technology as well as for multinationals in the U.S. and Japan.

Yet, Hu's predicament shows how powerful vested interests marshal law enforcement agencies to pressure foreign business executives, especially those who like Hu were once Chinese citizens but now hold foreign passports.