BOSTON — Condemned to die for his part in the 2013 Boston Marathon bombings, Dzhokhar Tsarnaev is likely to await his fate over the course of years, if not decades, locked up in grim prisons under extreme conditions while his lawyers appeal his sentence.

The U.S. Bureau of Prisons has not yet decided where Tsarnaev will go, but he is likely to end up in one of two high-security detention facilities, Colorado’s ADX or Indiana’s Terre Haute, according to U.S. District Attorney for Massachusetts Carmen Ortiz.

First the judge will hold a hearing where he will formally pronounce the sentence, Ortiz said after a jury decided on Friday that Tsarnaev, 21, deserved the death penalty.

He will then pass into the custody of the Federal Bureau of Prisons, which will determine where he should be held.

ADX, formerly known as the U.S. Penitentiary Administrative Maximum Facility, is likely “the most punitive, rigid, prison in America,” as defense lawyer Judith Clarke put it during Tsarnaev’s trial, arguing for life in prison for her client.

Life at the Florence, Colorado, prison is so difficult that prosecutors had worried jurors would vote for it as the harsher of the two sentences available to them, death or life imprisonment without possibility of release.

Imprisonment at the U.S. Penitentiary at Terre Haute would place Tsarnaev with other federal death row inmates and in the same complex where federal executions are carried out, said Robert Dunham, executive director of the Death Penalty Information Center (DPIC).

If ADX is known as the highest security prison for prisoners not sentenced to death, Terre Haute’s death row is “the most maximum security of maximum security,” Dunham said.

Tsarnaev’s death sentence, once confirmed at the hearing, would make him one of just 59 prisoners condemned to execution in U.S. federal courts, according to the Death Penalty Information Center.

If the sentence is carried out, he would join a group of just three federal prisoners executed since 1988, when capital punishment by the U.S. government was reinstated. In addition, 32 U.S. states allow the death penalty for state crimes, according to the DPIC’s website.

But Tsarnaev’s execution is neither imminent nor guaranteed. It will likely take at least a decade for his lawyers to exhaust all of his appellate options, said Dunham, and anywhere during the process, a court may overturn the death sentence, Dunham said.

“Because there is a death verdict, there will be a through appeals process,” he said. “If he had gotten a life sentence, this would be over with.”

ADX is located in the foothills of Colorado’s Rocky Mountains, but witnesses testified during Tsarnaev’s trial that inmates never see the majestic peaks nearby, getting only the occasional glimpse of sky during brief outdoor exercise periods.

At ADX, home to 416 male inmates, Tsarnaev would join some of the most infamous convicts in the United States, including Oklahoma City bomber accomplice Terry Nichols, underwear bomber Umar Farouk Abdulmutallab, and Unabomber Ted Kaczynski.

Tsarnaev would seldom see anyone else. Inmates spend an average of about 23 hours a day locked up alone in their cells, according to an audit of the U.S. Justice Department. There, they take meals passed through slots in the metal doors, watch prison television and write letters.

Each cell, under 24-hour surveillance, has a concrete bed, a table, a toilet, and a sliver of a window. A 10 foot by 20 foot outdoor enclosure slightly extends their world, but just for about an hour and a half each day, according to testimony by Mark Bezy, a former federal prison warden.

“They sit in their cells, locked in their cells every day,” Bezy said. Prisoners resort to communicating with each other through the pipes that link their toilets, he added.

No one has ever escaped from ADX, known as the “Alcatraz of the Rockies.”

ADX, founded in 1994, has been the subject of multiple lawsuits contending that sentences there violate constitutional protections against “cruel and unusual punishment.”

The federal government has housed condemned inmates since 1999 at a high-security institution in Terre Haute, a town of some 60,000 people in western Indiana.

The complex is home to the death chamber where all three prisoners executed by the federal government since 1988 have died by lethal injection, including Oklahoma City bomber Timothy McVeigh.

As in ADX, federal inmates at Terre Haute’s death row spend about 23 hours each day alone in small cells with a bed, a toilet and a wash station. Tsarnaev would live essentially in solitary confinement while his lawyers attempt to save him from death, Dunham said.

“Death row is supermax,” said Dunham. “It’s extremely, highly restricted.”