After a frenzied 33 hours to catch the suspected shooter of Charlie Kirk, prosecutors will unveil formal charges this week, providing their most detailed accounting yet of what happened and opening the next challenging chapter of the case.

Utah County prosecutors will formally arraign Tyler Robinson, 22, in court on Sept. 16, and they’ll have to sift through a mountain of interviews, photos, videos, and other forensic evidence to build the case against him.

Those charges will likely center on murder and are anticipated to leave the door open for the death penalty. Utah is one of 21 states that allows the punishment.

“Presumably, Robinson will be charged with murder for knowingly killing another person without justification, those are the elements of the crime,” said Paul Cassell, a law professor at the University of Utah. “Motive is not an element of the crime of murder.”

While some indications of motive could be included in the new court documents, Cassell said he expects prosecutors to initially focus on the opportunity, alleging Robinson was on the roof of a nearby building, and then hint at what drove him to allegedly fire at Kirk.

Utah Gov. Spencer Cox promised the state would pursue the death penalty in the case, but that decision will be made by Utah County Attorney Jeff Gray, with consultation from Kirk’s family. Prosecutors have 60 days to make that decision.

Sifting through evidence

With the day-and-a-half manhunt behind investigators, it's now their job to slow down and make sure they put together a case that meets the requirements set by courts and the law, said Katherine Schweit, a former FBI special agent and former Chicago prosecutor.

"It will take months and possibly years before everything is resolved," Schweit said.

Robinson's booking sheet indicated investigators are looking into Utah charges of aggravated murder, obstructing justice, and unlawfully discharging a firearm. As prosecutors mount a case, they will be sifting through evidence to find physical items and testimony that can support those – and potentially other – charges.

Public details suggest prosecutors already have a strong case, according to Neama Rahmani, a former federal prosecutor. If details revealed by Cox and FBI Director Kash Patel stand up in court, that includes surveillance video and DNA evidence linking Robinson to a towel and screwdriver tied to the crime.

"I expect there to be more biometric evidence, fingerprints, palm prints, shoe prints,” Rahmani said.

According to authorities, Robinson’s father also said his son confessed to the crime.

“It’s a pretty strong case in terms of, is he guilty or not guilty?” Rahmani said. That may mean the real challenge for investigators and prosecutors will come down to their potential pursuit of the death penalty.

Bringing a death penalty case

For the death penalty to apply, the state would have to prove one of several aggravating factors, such as how the suspect “created a great risk of death to another individual other than the deceased individual,” according to the state statute.

Cassell said prosecutors may have hinted at that strategy in their initial probable cause affidavit that pointed out Kirk was surrounded by a large crowd, including people immediately adjacent and behind him.

Utah prosecutors may point to the setting for Kirk’s killing in order to argue the shooting involved that aggravating factor, according to Rahmani.

“You're shooting into a crowd, right? It could potentially kill anyone,” he said.

Robinson and his attorneys will also get the chance to put on “mitigating” evidence designed to persuade a jury not to impose the death penalty. That kind of evidence can include the lack of a significant prior criminal history or a defendant’s youth.

In Utah, a jury must be unanimous to impose the death penalty.

Robinson is not cooperating with authorities, according to Cox. A death penalty case would also complicate his attorney appointment since court-appointed attorneys in those cases must have special qualifications.

Parallel state and federal tracks?

In addition to state murder charges, federal prosecutors could also charge Robinson on a parallel track, assuming they can tie the evidence to a potential federal crime.

The U.S. Justice Department did just that in its case against Luigi Mangione, who is accused of killing health insurance executive Brian Thompson on a Manhattan sidewalk. While New York authorities brought murder charges against Mangione that don’t carry a potential death penalty, federal prosecutors have charged him with using a firearm to commit murder and are seeking the death penalty in their case.

That could provide a backup plan if the state charges hit snags, said Cassell, echoing another famous Utah case.

“Elizabeth Smart’s kidnapping was the most high-profile in Utah history. The state prosecutor charged Brian David Mitchell with kidnapping, and the feds moved in and also charged him federally,” Cassell said. “The state charges did go awry, but because the feds had the federal kidnapping charge they could convict Mitchell.”

The Justice Department didn’t respond to USA TODAY’s request for comment on whether it will seek federal charges against Robinson.

Comparisons to Boston, Aurora

Patel, the FBI director, compared the rapid manhunt to that of the Boston Marathon bombing in April 2013.

The cases could be comparable when it comes to the scope of evidence collected. Authorities gathered 6,000 pieces of physical and digital evidence after the Boston attack; 100,000 photographs and videos, and more than 1,000 witness interviews.

The 10-week trial then introduced over 1,000 exhibits and called more than 100 witnesses to ultimately convict Dzhokhar Tsarnaev.

Former Assistant U.S. Attorney Aloke Chakravarty was on that prosecution team and said the Kirk case will need similar coordination across jurisdictions. They’ll also have to deal with the political and public noise around the case.

“Investigators will have to do a thorough investigation to answer not only who this suspect is, but also why and how he did it,” Chakravarty said. “They’ll be performing a comprehensive analysis of virtually everybody this person dealt with in the recent past.”

Chakravarty said local officials will likely lean on the FBI for forensic analysis to allow local authorities to do what they do best — connect and interview a web of contacts.

Colorado’s 23rd Judicial District Attorney George Brauchler successfully prosecuted James Holmes, the man who killed 12 people in the Aurora theater shooting in 2012.

The complex case will require discipline by prosecutors, he said.

“You have to get the rest of state government and investigators to button their lips, then the harder part is the feds,” Brauchler said. “Add to that the fact that you have a super accessible and transparent president. If he has information, he’ll likely share it.”

He said the uncharacteristically revealing media appearances by both Cox and Patel could complicate jury selection.

“If you don’t get the basics buttoned up, like pretrial publicity and evidence procedure, you’re setting yourself up for resource-sucking distractions,” Brauchler said, recalling a week-long setback for his case over a single notebook.

Evidence of motive?

There’s been a flurry of speculation about the suspect’s possible motives in the attack.

Cox has said Robinson had a “leftist ideology,” although he didn’t provide specific details about what the investigation has uncovered on that front.

As part of the investigation, authorities are likely trying to pinpoint that motive and may outline more in court documents on Sept. 16.

But proving a killer's motive isn't necessary to prove a murder case, the legal experts said. It can be helpful to showing an alleged shooter is the one who pulled the trigger, and that he did it intentionally.

“The motive can help us to understand and can help a jury understand that this person did intend to do something,” Schweit said.

This article originally appeared on USA TODAY: Mission change. Charlie Kirk shooting case moves from manhunt to the courtroom

Reporting by Nick Penzenstadler and Aysha Bagchi, USA TODAY / USA TODAY

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