BOISE - A 61-year-old man was arrested Thursday in New York City and has been charged in the death of Boise State University student Sierra Bush.

Boise police said Bruce Marchant, whose last known address is Boise, has been charged with murder, rape and kidnapping.

Sierra, who went missing in late September, was found dead at an outdoor location south of Idaho City on October 22. She was 18 years old.

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<p>Bruce Marchant (A mug shot from Ada County in November 2014)</p>

The Boise County coroner said Thursday that Sierra's death has been ruled a homicide, and that she died from some type of asphyxiation.

A first-year Boise State engineering student in the Honors College, Sierra - also known to many as "Simon" - was involved in a wide array of activities and clubs on campus.

RELATED: Sierra Bush honored by friends, family, Boise State community

Boise police said an arrest warrant was issued for Marchant on Tuesday.

On Wednesday, they received information that Marchant was in a New York City hospital. Detectives flew there to assist in his arrest.

Detectives are continuing their investigation in New York.

Marchant has a court hearing set for Jan. 5 in New York. The timeline for his extradition back to Idaho is unclear.

RELATED: Body of missing Boise teen found near Idaho City

Police said nearly 200 interviews have been conducted during the investigation, and that detectives from nearly every investigative unit in the department assisted and members of the BPD crime lab did extensive work that was instrumental in the arrest.

The Boise County Sheriff’s Office, Idaho County Sheriff’s Office, Boise County Coroner’s Office, Ada County Coroner’s Office and the FBI’s Behavioral Analysis Unit assisted.

Police are seeking to extradite Marchant back to Idaho.

Sierra's stepdad, Bart Green, issued the following statement to KTVB on Thursday:

"We have known for a couple days that this was coming. We want to extend our thanks to all of the Boise Police Department Detectives, uniformed officers and forensic technicians, the Idaho State Police crime lab workers, those at the Federal Bureau of Investigation, the U.S. Marshals Service and law enforcement agencies in other states for the role that each of them played in discovering and developing the evidence and in running to ground Sierra's alleged killer. There are so many professional law enforcement personnel, who we will never meet or get to thank in person, but that we know have worked very hard on Sierra's case. We are confident that the evidence against Sierra's alleged killer will lead to his successful prosecution and conviction. We look forward to that outcome so that there is some measure of justice for Sierra and so that the perpetrator is taken off the street for the rest of his life so that he will never have the opportunity to harm another person."

KTVB spoke with friends of Sierra/Simon on Thursday night who say they're relieved the suspect was finally caught, but finding out about the horrific things that happened to her is devastating.

"Having to face the reality of everything that happened has sort of put us in a big shock," Sierra's long-time friend, Evan O'Beirne, said.

He says he feels a sense of justice and finality, yet sadness and confusion.

"It just brings back basically everything, all the emotions we've been feeling the entire time," O'Beirne added. "When you lose a friend you can't just go back to normalcy. It's the hardest thing, when we live with all of that every day."

Since Sierra/Simon's body was found in October, O'Beirne says he and his friends have had their ideas about what happened, but when they learned about Marchant being charged with rape, it solidified their fears.

"We hoped more than anything that she didn't suffer, that it was over quickly," O'Bierne said. "Realizing that this actually did happen is more of what's getting us down than anything else."

O'Beirne told KTVB Sierra's loved ones needed to know the identity of this person.

"And as soon as we found out, [we were] like, 'who is this?' We have no idea, we've never heard this name before."

O'Beirne says the fact that the suspect is a stranger just shows there was no need for any of this. He says to get any sense of closure, it's necessary her friends get answers.

"There are things we're going to find out that we probably aren't going to want to, but we need to," O'Beirne said. "We need to know what happened and why."

For Sierra's family's sake, O'Beirne hopes justice is served to her alleged killer.

"Why was it worth it? Why would you do this to everyone: this entire community you see unfolding before you, everyone that loved her? Why would you do this?"

There are still many unanswered questions about Sierra/Simon's disappearance and death at this time. Many people are wondering where she was abducted, why she was taken, and if there is any connection between Bush and Marchant at all. As soon as those answers become available, we will bring them to you.