For nearly a year, six Chinese crew members on a ship that crashed into the San Francisco-Oakland Bay Bridge — creating the bay's worst oil spill in nearly 20 years — have been detained by federal authorities.

The sailors are being held as material witnesses in the crash of the Cosco Busan. The men, including four who are not accused of wrongdoing, are fighting for the right to return to their families in China.

"This is a lengthy detention," said University of Georgia law professor Ronald Carlson, an expert on the material witness law. "These witnesses are being detained humanely. Still, there is that undeniable desire to return home."

The 900-foot cargo ship sideswiped a bridge support in heavy fog, gashing its hull and leaking more than 50,000 gallons of fuel that killed and injured thousands of birds. It was believed to be the biggest San Francisco Bay oil spill since 1988.

Prosecutors want the six to testify in criminal cases against the harbor pilot, John Cota, and the ship's Hong Kong-based operator, Fleet Management Ltd. Both have pleaded not guilty.

Although they are under arrest as material witnesses, they are not in jail.

Living rent-free in apartments and hotels, they are permitted to roam San Francisco and the surrounding area. They continue to draw their salaries, and each also receives $1,200 per month in witness fees, more than the monthly salary of at least one detained seaman.

Chinese officials here hope the crew can return soon. But "we believe they are situated pretty well," said Defa Tong, a spokesman for the Chinese consulate in San Francisco. "Some of them are going to school to learn English."

Still, the men have been unable to celebrate family birthdays and tend to sick relatives. One crewman's wedding had to be delayed.

"They are unhappily detained," said Douglas Schwartz, a lawyer representing the ship's captain, Mao Cai Sun.

The crew's legal predicament stems from federal law allowing the arrest of witnesses who might flee before testifying in criminal cases. Several other countries, including the United Kingdom, have similar laws.

Two of the six crewmen have admitted wrongdoing. Shun Biao Zhao, the ship's second officer, has admitted altering and forging navigational documents after the crash. Kong Xiang Hu, the chief officer, admitted signing one of these documents. Both men contend Fleet executives ordered the alterations and signings, which the company denies.

All six have been granted protection from prosecution if they testify truthfully.

In defending the lengthy detention, Assistant U.S. Attorney Jonathan Schmidt said the crew members' "evasiveness and participation in obstruction of justice" were factors.

The crew's lawyers declined to make the men available, citing their legal situation.

Although the trial is scheduled for April, the government recently agreed to let the crew have their testimony videotaped. Two of the six have already taped their testimony, and the rest are due to wind theirs up by the end of December.

The crew's lawyers want the judge to let the men return home after completing their depositions, and the two who already have are due to make that request on Friday.

But federal prosecutors also want some of the six to testify in a suit against the ship's owners. While the law on holding material witnesses doesn't apply in civil cases, a subpoena in the civil suit could still complicate their departures.

Cota, who was at the controls when the ship crashed, is charged with lying on medical reports required by the Coast Guard. Fleet Management is charged with ordering at least one of Chinese crew member to alter documents after the accident. Both are also charged with environmental crimes.

Most of the roughly 3,000 people arrested each year on material witness warrants are illegal immigrants who are held until they can testify against their human smugglers, legal experts said.

After the Sept. 11, 2001, terrorist attacks, federal authorities arrested dozens of Muslim men as material witnesses connected to terrorism. Some of those detentions lasted several months and never resulted in charges, and civil libertarians criticized the Bush administration's use of the law.