A retired Nevada law enforcement expert who served on the FBI Joint Terrorism Task Force said modern technology can complicate the effort to discover the killer's motive for the shooting at former President Trump's Pennsylvania rally.

Ashton Packe, a former Las Vegas police detective, shared the roadblock that investigators may be encountering while working to gain access to Thomas Matthew Crooks' cellphone.

The FBI said Sunday night it had obtained Crooks' phone for examination after the 20-year-old attempted to assassinate former President Trump at a Butler, Pennsylvania, rally on Saturday.

A senior FBI official confirmed to Fox News on Sunday night that while they believe the shooter acted alone, they had not been able to get into his cellphone.

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"Today in modern day America, criminal investigations just inherently require the access or the use of these digital devices," Packe told Fox News Digital. "No crime is committed without the criminal having evidence on a cellphone or some kind of digital device. 

"The problem comes with trying to break into the device," he said.

Packe, who was on an FBI task force, said getting into an encrypted device proves to be difficult – even if Crooks' phone is in the hands of the country's top agents.

"Getting into an encrypted locked device, in today's age, is incredibly difficult," he said. "Certain companies, like Apple, can get into any of these devices."

He said gaining access to Crooks' locked phone would require that U.S. agencies get the help of "foreign adversaries" or "foreign nation state people."

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"Are there parts of the government where you can probably get into certain phones? Absolutely," he said. "But that involves non-U.S. citizens and outside the continental United States."

"So foreign adversaries, foreign nation-state people," he said. "You're talking high-level spy games there. Those are not tools that will be used by civilian law enforcement here in the United States, no matter what the conspiracy theorists say."

Packe said that if the FBI attempts to decrypt Crooks' cellphone, it could be a "catch-22."

"But depending on the level of encryption that the phone has, they might be able to get into it, which is a catch-22," he said. "Here in the United States, we all have the right to privacy and the right to be safe and secure in our person – and that is guaranteed under the Fourth Amendment."

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"So law enforcement has to get a search warrant for that, but civilian law enforcement won't be able to find out what's in there unless they have that passcode," he said.

Packe shared his opinion after Kevin Rojek, FBI special agent in charge in Pittsburgh, said "the information that we have" indicated that Crooks acted alone.

"At this time, the information that we have indicates that the shooter acted alone and that there are currently no public safety concerns at present," Rojek said in a press conference on Sunday.

"We have not identified an ideology associated with the subject, but I want to remind everyone that we're still very early in this investigation."

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When asked by Fox News if the FBI knew Crooks' phone company, Rojek said, "We're not going to be in a position to disclose the service provider in the phone at the station."

On Monday, the FBI confirmed that House Judiciary Chairman Jim Jordan, R-Ohio, and ranking member Jerry Nadler, D-N.Y., received an FBI briefing about Crooks' phone.