In 2015, a jury convicted James Holmes of carrying out the Aurora, Colo., movie theater shooting rampage. The same jury then sentenced him to life in prison for killing 12 people and wounding dozens of others during the massacre.

Not long after that, however, Holmes effectively disappeared. His location was not publicly known for nearly two years after officials transferred him to a prison outside Colorado and refused to say where he was being held, which angered survivors of the attack and prosecutors alike.

This week, that question was finally answered. Holmes, 29, is being held at the federal penitentiary in Allenwood, Pa., according to Federal Bureau of Prisons records. The high-security facility, which houses only male inmates, is located 165 miles northwest of Philadelphia.

Colorado officials said Wednesday that they had tried to place Holmes in a federal facility months earlier but were unable to find space at a place they described as having the necessary security. They did not say where Holmes had been held until he was transferred.

“The Colorado Department of Corrections confirms that inmate James Holmes has been transferred to a federal prison,” the department said in a statement. “The State sought to place the inmate in the Federal System several months ago, but placement required finding space at a facility that could provide appropriate security. That space recently became available and the move to the Federal prison was secured.”

Holmes’s location had been a mystery since early 2016, when state officials acknowledged that he had been moved out of Colorado. They would not say where he was transferred, pointing to safety concerns. The state prisons director later said that part of the reason Holmes was moved was because he had been attacked by another inmate.

Victims of the movie theater attack filed complaints, arguing that their rights were being violated by not knowing where he was being held. A state committee was split over whether victims of the shooting had a right to know where he was, and earlier this year, the committee said the corrections department should have done more to keep victims informed, including telling them more about why Holmes’s location was not being revealed.

The mystery of Holmes’s location also stood out because in other high-profile cases involving recent mass attacks — some of which went to trial not long before or after the Aurora shooting — inmates’ locations have been made public.

Dzhokhar Tsarnaev, who was convicted in 2015 for his role in the Boston Marathon bombing and sentenced to death, is being held at the Florence, Colo., supermax prison. Dylann Roof, who was convicted last year for the Charleston church massacre and sentenced to death, has been moved to the federal penitentiary in Terre Haute, Ind., which is where federal death sentences are carried out.

Tsarnaev and Roof — who, like Holmes, were young men charged with carrying out violent attacks in public places — both faced federal charges. In both cases, federal prosecutors sought and won death sentences, though it remains unclear if either will be executed; the federal government very rarely carries out death sentences.

Holmes was charged in state court and, after an emotional extended trial, found guilty on each of the 165 charges he faced. His attorneys had not denied that he carried out the shooting, and instead Holmes pleaded not guilty by reason of insanity. Lawyers for Holmes argued that he was having “a psychotic episode” when he began gunning down moviegoers gathered for a midnight screening of “The Dark Knight Rises” in July 2012.

After convicting him, the jurors ultimately spared him a death sentence, instead deciding that he should spend the remainder of his life in prison. A unanimous vote was needed to sentence Holmes to death, and at least one juror was said to have been adamantly opposed to such a punishment. (Death sentences are unusual in Colorado, one of the country’s least active death-penalty states.) Holmes was formally sentenced to 12 lifetimes in prison.

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