NEW YORK -- Complaints about security and its high costs forced the Obama administration to reconsider a decision to try the professed Sept. 11 mastermind in Manhattan, but the first civilian trial of a Guantanamo Bay detainee is moving ahead there anyway.

Opening statements are likely to begin Tuesday with experts divided over whether the terrorism trial of Ahmed Khalfan Ghailani should open the door to a civilian trial for Khalid Sheik Mohammed and others held at Guantanamo Bay or slam it shut.

Attorney General Eric Holder announced in November that Mohammed would be tried in Manhattan, only to later withdraw the plans after critics said trying him there would tax the city emotionally and come at great security cost.

Ghailani, 36, is charged with conspiring with others, including Usama bin Laden, to blow up two U.S. embassies in Africa in August 1998. The attacks killed 224 people, including 12 Americans. If convicted, Ghailani could face life in prison.

Prosecutors will proceed without their top witness after U.S. District Judge Lewis A. Kaplan ruled last week that the man's testimony that he sold explosives to Ghailani must be excluded because the government only learned about him after Ghailani was interrogated at a secret overseas CIA camp after his 2004 arrest where harsh interrogations occurred.

Ghailani, a Tanzanian, was arrested in Pakistan. The government has chosen not to use at trial statements he made after his arrest, unless Ghailani testifies. Ghailani has been accused by the government of being a bomb maker, document forger and aide to bin Laden. He has denied knowing that TNT and oxygen tanks he delivered would be used to make a bomb.

Losing some evidence against Guantanamo detainees is a hazard the government must weigh in its quest to try them in civilian courts, experts say.

Fordham law professor Annemarie McAvoy, a former federal prosecutor with expertise in terrorist financing, said Ghailani's trial could cause the U.S. Congress to review how civilian trial rules are applied.

"Nobody really knows what the right thing to do is. We've never been in this situation before," she said, noting she supports military tribunals over trials. "This is an evolving process that hasn't reached a point yet that is perfect. That's for sure. There'll be some false starts, changes in legislation. It all takes time."

She added: "If anybody walks away without a conviction, we will, as a country, look horribly inept."

Barry Mawn, who retired after leading New York's FBI office at the time of the Sept. 11, 2001, attacks, said he thinks where detainees are tried should be decided on a case-by-case basis. He said it makes sense to try Ghailani in court because the evidence was gathered with an eye toward prosecuting the case.

Aitan Goelman, a former federal terrorism prosecutor now in private practice in Washington, predicted the Ghailani case will impact where other Guantanamo detainees will be tried.

"If something goes dramatically wrong, that could be relatively devastating," Goelman said. He said the government needs to establish clear rules about the circumstances under which detainees will be tried in civilian courts.

The Ghailani trial is the second trial in Manhattan to stem from the embassy bombings. Four men convicted at a 2001 trial are serving life sentences.

Federal court in Manhattan has hosted more than a half-dozen major terrorism trials since the Feb. 26, 1993, World Trade Center bombing that killed six people. The trials have resulted in convictions for those charged in plots including that bombing, a 1993 plot to blow up five New York landmarks and a 1995 plot to blow up 12 U.S. airliners over the Far East, among others.

Just last week, Faisal Shahzad was sentenced to life in prison for trying to blow up a homemade car bomb in Times Square on May 1.

This week, a jury continues deliberations in the trial of four men accused of plotting to detonate explosives near a synagogue in the Bronx and to shoot Stinger surface-to-air guided missiles at military planes.