In response to questions at his September 10 press conference, President Obama spoke about his failure to fulfill his clear campaign promise to close the military prison camp at Guantánamo Bay, Cuba. He blamed fear and “political rhetoric” for blocking his plan to move Gitmo detainees to prisons in on U.S. soil. In the course of discussing Guantánamo, Obama said:

And by the way, just from a purely fiscal point of view, the costs of holding folks in Guantánamo is massively higher than it is holding them in a supermax maximum security prison here in the United States.

There’s no question that the president’s statement was true. The trouble started when the federal Bureau of Prisons was asked to provide information on the cost of holding a prisoner in a U.S. supermax. The Miami Herald‘s Carol Rosenberg followed up on the numbers. In an article following the press conference, she wrote:

Pentagon reports the annual cost of running the prison camps, staffed by a variety of U.S. military troops, at $116 million. With a current population of 176 war-on-terror detainees, that’s more than $650,000 each.

By contrast, it costs nearly $5,575 a year to keep a prisoner in federal detention, said Bureau of Prisons spokeswoman Traci Billingsley on Friday. A Supermax prisoner’s cost might be a bit higher, she said, because of additional security.

That just didn’t sound right to us–neither the $5,575 figure, nor the fact that supermax costs would only be just “a bit higher.” And sure enough, a few days later Rosenberg reported: 

A Bureau of Prisons spokesman on Monday revised upwards the cost of housing a captive in federal detention, days after the bureau said it spends a tiny fraction of what the military spends at Guantánamo Bay.

The new figure — $27,251 a year per federal prisoner compared to $650,000 per captive at the U.S. base in Cuba — is still a tiny fraction. “Obviously we’re far less expensive than what the military is doing,” said Bureau of Prisons spokesman Edmond Ross.

The per prisoner cost has exceeded $25,000 for several years now in the federal system, he said. It was unclear how a colleague arrived Friday at $5,750 a year, he said.

Now, $27,351 may still be a “tiny fraction” of what’s spent at Gitmo–but multiplied by more than 200,000 federal prisoners, it’s still a lot of money. More importantly, it’s still not an accurate figure for the cost of keeping a supermax prisoner–something the BOP spokesperson neglected to mention when he provided the “corrected” number.

If the Bureau of Prisons wished to provide an accurate projection of costs, it could have provided figures for ADX Florence, the notorious federal supermax in Colorado, or for the “Communications Management Units” (CMUs) at Marion or Terre Haute federal penitentiaries– the units that most resemble any proposed future home for Guantánamo detainees. Yet it chose instead to offer the media misleading lowball figures.

We do know that the average annual cost for a supermax prisoner, according to one study by the Urban Institute, is $75,000 a year, as opposed to $25,000 for a prisoner in the general population. At the Illinois State Tamms supermax, it’s about $92,000 a year.

And this does not take into account the cost of building supermax prisons in the first place. The price tage for ADX Florence, completed in 1994, was $60 million, and it houses only about 400 prisoners. Obama’s proposed future home for Gitmo detainees, an unused state prison in Thomson, Illinois, would cost $237 million to buy, retrofit, and activate.