FBI Director Christopher Wray has disturbing news for House lawmakers regarding its efforts to extract key criminal evidence from smartphones — they don’t have the know-how.

The FBI is struggling to decode private messages on phones and other mobile devices that could contain invaluable information, and the agency failed to access data more than half of the times it tried during the last fiscal year,

According to his prepared remarks, Wray will testify before the House Judiciary Committee on Thursday morning about issues currently facing the FBI, including its ability to keep up with technology.

“The rapid pace of advances in mobile and other communication technologies continues to present a significant challenge to conducting lawful court-ordered access to digital information or evidence,” said Wray. “Unfortunately, there is a real and growing gap between law enforcement’s legal authority to access digital information and its technical ability to do so.”

Criminals and terrorists are using these technologies, he warned, noting that the Islamic State is reaching potential recruits through encrypted messaging. This causes problems for law enforcement agents.

“If we cannot access this evidence, it will have ongoing, significant effects on our ability to identify, stop, and prosecute these offenders,” he warned.

Regardless of their legal authority, the FBI was unable to access data on approximately 7,800 mobile devices last year, revealed Wray. He added that the number represented a little more than half of the mobile devices the FBI tried to access in fiscal year 2017.

The FBI needs to keep up with technological advances, Wray emphasized. “When changes in technology hinder law enforcement’s ability to exercise investigative tools and follow critical leads, those changes also hinder efforts to identify and stop criminals or terrorists,” he said, noting that the agency is working with experts to find “solutions to this problem.”

Wray is likely to be questioned on a wide range of topics at Thursday’s hearing, including new complaints from Republicans that Wray and other Justice Department officials have ignored requests for information about their actions in the Russia election-meddling probe, according to a report in The Washington Examiner.

Republicans have started writing a contempt resolution against Wray and others this week after the Justice Department failed to answer questions from lawmakers about why a top FBI agent was removed from the Russia probe. It was later discovered that the agent sympathized with Hillary Clinton and wrote disparaging comments in notes to his mistress about then-presidential candidate Donald Trump.