Sen. Ben Nelson (Neb.) became the fifth Democrat to join ranks with Republicans seeking to stop the Obama administration from trying 9/11 terrorists in U.S. courts.

In a statement Wednesday, Nelson said he has decided to co-sponsor Sen. Lindsey Graham’s (R-S.C.) bill to prohibit the Justice Department from using federal funds to prosecute 9/11 conspirators in New York City, as Justice had planned.

Though Justice is reportedly already reconsidering holding terrorist trials in New York, the issue of what to do with hundreds of suspected terrorists at the Guantánamo Bay, Cuba, military prison has bedeviled the Obama administration since Day One. With President Barack Obama’s vow to close the prison, the Justice Department announced last month that it was seeking funding to buy an Illinois state prison facility to house suspected terrorists.

“I am pleased that President Obama is reconsidering his plan to hold these trials in New York,” Nelson said. “In a time when we are facing astronomical budget deficits, our national security calls for us to make smart decisions about spending. We must find a solution for the prosecution and detention of those at Guantanamo that does not expose us to overwhelming financial burdens of potentially a billion dollars and heightened security risks for Americans.”

Nelson said he would prefer the administration take 9/11 terrorist cases before military commissions because of the security risks and costs to taxpayers.

“Last month, New York City Mayor Michael Bloomberg sent a letter to President Obama detailing just how significant the costs of the trial would be and requesting that the federal government cover these costs. He estimated that the costs of detaining and trying the men would be $216 million in the first year and an additional $200 million each subsequent year. Since then, even those estimates have sky rocketed to as much as a billion dollars,” Nelson said.

Nelson notes that in addition to Bloomberg, New York Democratic Sens. Charles Schumer and Kirsten Gillibrand, along with Gov. David Paterson, oppose holding the trials in New York. Schumer and Gillibrand, however, have not become co-sponsors of the Graham bill.

Graham’s bill to prohibit the Justice Department from using any funds to pay for the civilian prosecutions is supported by 21 other Republicans. Democratic Sens. Blanche Lincoln (Ark.), Mark Pryor (Ark.) and Jim Webb (Va.) and Democratic-leaning Independent Joe Lieberman (Conn.) have also co-sponsored the bill.

The measure would only affect the trials of those suspected of planning and participating in the Sept. 11, 2001, attacks on New York and Washington, D.C.