The FBI has confiscated the phone of the gunman who opened fire at a Texas church Sunday but is unable to access it for the ongoing investigation, an official revealed Tuesday.

FBI Special Agent Christopher Combs, who is leading the investigation, told reporters that the bureau had flown the device to Quantico, Va., Monday night and that agents have been reviewing the phone but have not been able to get into it.

“It actually highlights an issue that you’ve all heard about before with advance of the phones and the technology and the encryption, law enforcement, whether it’s at the state, local or the federal level, is increasingly not able to get into these phones,” Combs said at a press conference on Tuesday.

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“I can assure you that we are working very hard to get into the phone and that will continue until we find an answer. I don’t know how long that is going to be,” Combs said. “It could be tomorrow, it could be a week, it could be a month.”

Combs’s remarks harkened back to those made by Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE just last week as he lamented the terror attack in New York City that killed eight people.

Sessions said the FBI was unable to access nearly 7,500 mobile devices they had seized as evidence in ongoing investigations “even though there was court orders or legal authority to do so.”

"This failure to get encrypted information in a timely manner causes law enforcement to waste even more valuable time and resources,” Sessions said in New York on Thursday. “And it could have potentially deadly consequences.”

It is unclear the type of phone that shooter Devin Kelley used, which is now in the possession of FBI agents. Combs made a point not to describe the type of device on Tuesday.

The issue of law enforcement access to encrypted evidence has become a point of tension between federal authorities and technology companies over concerns about data privacy.

Last year, the FBI solicited help from professional hackers to unlock an iPhone used by one of the shooters in the 2015 San Bernardino terror attack after Apple refused a federal request to unlock the device.

Kelley opened fire at First Baptist Church in Sutherland Springs on Sunday, killing 26 people in what is the deadliest mass shooting in Texas history.