A slain terror suspect’s Apple iPhone has presented problems for the FBI yet again, this time in Minnesota where a familiar obstacle has complicated the investigation into the man who stabbed 10 people inside a St. Cloud shopping mall last month.

FBI Special Agent Rich Thornton told reporters on Thursday that authorities have obtained 780GB of data from computer and other devices owned by Dahir Adan, a 22-year-old Somali-American who conducted the Sept. 17 stabbing spree before being shot and killed by an off-duty police officer.

Investigators are reviewing Adan’s social media accounts and past internet activity, and have filed search warrants and subpoenas in an effort to acquire any additional clues that could help them make sense of the stabbings, Mr. Thornton said. Just as in the wake of the mass shooting in San Bernardino last December, however, investigators have found themselves once again struggling to acquire information off their slain suspect’s cellphone.

“Dahir Adan’s iPhone is locked,” Mr. Thornton told reporters, “We are in the process of assessing our legal and technical options to gain access to this device and the data it may contain.”

In both the St. Cloud stabbings and last year’s mass shooting, investigators attempted to find evidence in the aftermath that could show a nexus between the perpetrators and foreign terrorists. The Islamic State took credit for both attacks, but has attributed itself before with incidents committed by copycats, sympathizers or individuals with no direct ties to the terror group.

The contents of Adan’s iPhone could potentially reveal the existence of any communications he had with terrorists using social media or messaging apps, and the FBI may soon ask a federal judge for Apple’s help if it follows the same plan as during the San Bernardino probe.

Syed Farook, half of the married couple responsible for the rampage in southern California, had enabled security settings on his iPhone 5C that prevented investigators from unlocking it for several months. The Department of Justice eventually contracted an outside party to hack its way into Farook’s iPhone, but not before taking Apple to court and igniting a heated debate about the limits of security and privacy.

The FBI hasn’t divulged the specific iPhone model owned by Adan, but mobile devices running any of the operating systems released by Apple in the last two years include security mechanisms intended to prevent unauthorized access. A company that brokers security exploits recently said it will pay $1.5 million if a hacker can show them how to compromise a supposedly secure iPhone running Apple’s latest operating system, iOS 10.

Neither the FBI nor Apple responded to requests for comment when contacted by WIRED following Thursday’s briefing.

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